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Accusump Failure Immediate total Oil loss

RV7DES

Member
I have just had my plane lose all its oil just before shutdown when the accusump blew its top. Has anyone had this issue? I lost almost all the oil in a few seconds. If it happened during flight I would be going down.

So far Canton has said maybe I shouldn't fit a valve direct to the accusump, and maybe the vibrations caused the top to seperate. However I am not impressed by the thickness of the unit around the tread, and believe it was an issue waiting to happen, and would not be happy fitting one again until I know why. I'd like to share this with as many others that have these units fitted. Until this failure I loved the system, and have done lots of aeros.

Im including my initial report to Canton and would welcome another thoughts. It was very fortunate this occurred 10sec before shutdown.

I'll include photos as soon as I can.

**************

Accusump top separating from body while engine running

Engine : IO-360 aircraft
Hours total 1200
Accusump fitted March 2013 with approximately 350hours flown
Electronic valve fitted Nov 2016 with approximately 20 hours flown since fitting

On 20th of Jan 2017 at around 10am I left Te Kowhai for a 30min flight to Tauranga.
While preflighting I switched the electronic oil valve to on position to pre oil the plane for around 2min. Shut the valve off and started the plane.

The flight was normal lasting around 30min reaching no higher than 3000ft before landing in Tauranga. A few minutes before landing pre landing checks indicated the engine running fine and oil pressure normal. Some 30m before shut down a loud bang occurred and I shut down the engine. The following fault was found.

The Accusump had separated at the top and almost all oil from the engine was lost.

If this had occurred at anytime during the flight the plane would have required an emergency landing with the possible loss of life. Other planes around the world are fitted with these units, and and there is a grave concerned that this could occur again.

During the whole flight the valve had been left off to allow maximum oil to flow throughout the engine. The accusump was installed for aerobatic flight and to insure the engine has oil when any negative g forces occur.

24-046 - ACCUSUMP 1QT NO VALVE

24-270X - ACCUSUMP PRO ELECTRIC VALVE KIT

All components were fitted by qualified aircraft engineers and according to manufactures instructions.

***********

On testing the value with air, we found the valve when closed (as I had it) is letting air through into where the accusump was but not letting it out. This would account for the total oil loss after the incident.
 
M5DKR
 
I'm glad you were on the ground and shutting the engine down. Now it is just a PITA. I have the Moroso 1.5 qt accumulator, about 165 hours and electric valve mounted on top. No issues so far, and haven't heard of any issues with any accumulators. I don't see how the valve being mounted on top would be a factor in the failure of the unit. That aluminum does seem really thin though.
 
Clearly the problem originated from the flames.:D
Glad you are down safe.
 
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The accumulator should not exceed the oil pressure of the engine. My accumulator is showing 60 psi on the preflight, and I keep it open during short flights. Long flights I use it as a emergency oil source if I should start losing oil pressure.
The oil pressure seen in our engines should never be able to blow that apart the way that unit failed.
 
Looking at data nothing out of the ordinary regarding oil pressure. Didn't have a release valve on the Accusump. When I close the valve and shut the engine down the accusump reads around 160psi on its meter. I've been told this is normal due to it being air pressure not oil. I can't see my engine producing that much pressure. Yes the thickness is an issue and I'm not confident this would not happen again if I selected the same brand. Until this happened I thought everything was fantastic. Accusump does give some real advantages. I had checked the system 10 hours after the valve was fitted with no evidence of fatigue.
 
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Pressure is pressure. If your engine oil pressure is 70, the accumulator pressure should be equal to that. On the Moroso accumulator, the unit is charged with 10 PSI of air as a precharge, but after that, it is the engine oil pressure that determines the accumulator pressure. I would check your engine monitor to see if you are getting unusually high oil pressure somewhere along the way.
There are a bunch of us using accumulators on this site, and I'm sure they know more about engines than I do, so I would be interested in their opinions.
 
vibration?

I can't quite see from the second photo, but it seems like there is a lot of unsupported mass connected to the top of the unit. That 1/2" flex hose and the metal object underneath don't seem to be clamped to the firewall. Could that have been what caused the problem?
 
Did the canister break directly under the band clamp? It appears that way. wondering if it was at the base of the threads, and through motion took 350 hours to crack its way through.

Tom
 
Dan,
What about the 160 psi reading on the accumulator? Also, if it were a fatigue related issue, wouldn't the metal have to experience some type of flexing?
 
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Michael---160 sounds like its way to much to me. Back in the racing days, we had a Moroso accumulator, but I think 60 psi is what we use to run. So, 160, and the fatigue of the cylinder could have caused this.

I'm sure there are some smart guys working on this.
Tom
 
I spoke with Moroso today, and was informed the burst pressure on my unit is 500psi. They have a heavy duty unit that will handle 2,000psi, but I think that is an overkill.
 
Dan,
What about the 160 psi reading on the accumulator?

First check the gauge, obviously. If accurate, the only reasonable conclusion would be that (1) the canister had very little air charge, and (2) was subjected to a temperature rise after it was filled.

Consider the OP's statements:

While preflighting I switched the electronic oil valve to on position to pre oil the plane for around 2min. Shut the valve off and started the plane.

Ok, the accumulator emptied, then the valve is closed before a cold start...

During the whole flight the valve had been left off to allow maximum oil to flow throughout the engine.

...and remains closed for the entire flight.

On testing the value with air, we found the valve when closed (as I had it) is letting air through into where the accusump was but not letting it out.

When closed, the valve will pass fluid one way, into the canister, but won't let it out.

The cold start pumps the canister entirely full of cold oil. Later, while in flight, the trapped cold oil is heated to a temperature near lower cowl air temperature, perhaps higher if exposed to radiant heating. Oil subjected to a temperature rise of 100F would expand about 4%, which is no problem with an air chamber to allow piston movement. Lacking air, a tube entirely full of trapped oil would see a significant pressure rise.

Although it might explain the post-flight gauge reading, 160 psi alone should not be enough to fail the canister. If I read correctly, it is normally fitted with a 175 psi pop-off, and would be designed for a good margin above that.

Also, if it were a fatigue related issue, wouldn't the metal have to experience some type of flexing?

Yes, but perhaps not the way you're imagining. The part need only be subjected to stress cycles, which may or may not result in movement apparent to the naked eye.
 
Thank you for the replies.

The clamp was over the thread and the area that failed. I am sure the extra weight of the valve didn't help the fatigue however what concerns me is that I can measure around 0.8mm of metal where it likely failed. The other side has 1.3mm. Even without the valve on top was it an accident waiting to happen?

The 160psi was something I question, however another unit recently fitted to a friends RV reads 140psi at idle. How do others who have the accusump read while idling, or if they have the valve fitted what do they read after shutting down?

The recharge was at 10psi and checked regularly. (Not accounting for a possible faulty valve.

The closing of the valve I would have thought would would stop oil from going into the accusump as well as out. I can see how as I start up with the valve closed the accusump pressurised with cool oil which couldn't release causing more pressure. Is this a faulty valve?

Still does not get over the fact there is so little metal between the tread and external case.

http://imgur.com/a/sq8ql

I'm really appreciating the feedback.
 
What if, even with the 10 PSI pre-charge, the piston is pushed to the top of the accumulator with cold oil. Wouldn't the air pressure gauge stop going up because the piston can no longer move, but the the fluid pressure continues to rise with tempeture until failure? Just thinking out loud:eek:
 
The psi readings, are they with the valve open? The tech I spoke with at Moroso said the pressure reading if the valve is open, should be what the engine is reading. If the valve is closed, I can see the point that Dan was making, as far as the air and oil expanding in a closed container.
 
Location, location, location.

Perhaps.... the clamp was just a touch too low on the tube. I can't really see from the photos, but if either higher over the threads and more of the end cap, or else much lower away from the threaded area of the tube, you might not have had this failure. This is only a guess as I can't really determine where the clamp was located on the tube and end cap before the failure by the photos provided. I am quite certain that type of clamp can crush and deform a thin wall tube. Try a section of AL tubing with open ends. Use various amounts of torque and measure the ID with an inside micrometer or T-Scope gage and outside mike.
 
When the valve is shut after closing while downwind and the oil was hot the meter would read up to 160psi. When the same charge is cool it would read around 100 - 120 psi.

The base of the tread was around the middle of the clamp
I'm not sure if it was over tightened however I don't believe there was any indentation in the tube. I will get the micro meter out when I'm back in the workshop tomorrow NZ time.

I also am not sure if the valve was functioning properly.

Sounds like a number of factors
 
Following Closely

I'm following this thread closely as I'm sure are many other accumulator users. My Canton 2qt Accusump has been installed for over a year and I've put about 110 hours on it. I've found it very effective on my RV-4 during aerobatics. I don't have a full inverted oil or fuel system - just a carb, a 1/2 Raven and the Accusump. During inverted flight, the accumulator does a good job of maintaining oil pressure above about 30 psi for up to about 10 seconds. Of course, my engine quits during those 10 zero to negative G seconds so I'm not producing much power anyway!

Thank you RV7DES for putting up all the information on this failure. I hope you will keep the information coming, especially if you hear any more from Canton.

Based on the evidence presented, this is clearly a fatigue failure. The cause is less easy to discern but I agree with Dan that, especially in the high vibration area of the engine compartment, the long arm of the valve and connecting piping probably imposed a significant load on the accumulator at the cylinder / band intersection. The method of operation and the lack of a relief valve are also probably contributory.

I'm very surprised that no pressure relief valve was installed. Why not? The pressure relief valve is a very important part of the design and should be in place in all installations. There are several situations and failure modes that can result in excessive pressures in the accumulator. The pressure relief valve is designed to prevent a catastrophic failure during those cases. From the manual:

"The patented safety pressure relief valve is to protect the unit. In cases where the unit is set up incorrectly and/or there is a leak in the airside of a unit, it could become Hydraulically locked (totally full of oil). Under this condition, if the unit is heated the safety valve will open, releasing the excess pressure and protecting the unit. If this does occur you should be aware that there is a problem and you should review your AccusumpTM setup as described in this manual."

Placing the accumulator inside the engine compartment also increases the risk of failure. High temperatures and vibration are both detrimental. Temperature is probably the worse of the two. There are numerous cautions in the Accusump manual about locating the unit in a high heat area. When the main valve is closed, if, for whatever reason, the air charge is lost while the accumulator is full of oil, as temperature rises, the expanding, incompressible oil has only one outlet - the pressure relief valve. Without a relief valve installed, a cylinder burst would be a predictable failure mode, especially at a point of physical stress. My accumulator is installed aft of the firewall so it does not encounter the harsh temperature / vibration environment in the engine compartment. I also have the factory installed pressure relief valve in place. The disadvantage of my installation of course is that, should I experience a failure, there will be some oil in the cabin.

There's a lot going on here and much conflicting information. RV7DES got a lot of good service out of his accumulator but had a nasty failure. There are some obvious possibilities but, as with most accidents / incidents, there are probably a number of factors involved in this event.

Personally, I'm very happy with my accumulator and it's been trouble free. It's important to pay close attention to the installation and operating instructions and especially the cautions if you choose to use an accumulator. This is definitely an "off label" use as far as the manufacturers are concerned! I don't think you'll find any of them advertising their accumulators for use in airplanes.
 
My theory.

Edit 1-26 I re-read the op and DanH's post. Then I felt a John Thocker dope-slap to the head for reading comprehension.

I agree with DanH completely. To add - The operation of the valve as a check valve is the root cause of the failure. There are pressure variations in that hose due to the positive displacement gear pump. The check valve will clip the peaks and reflect the max of these ultimately. This will occur when the oil is coolest.

More on the dimensions of the piston would be helpful. I think it is dished on both sides with a double o-ring. It is entirely possible that at or near 160 psi the air space is so small so as to allow the piston to go solid. Then the air side is fixed and the oil side could be 500 psi with taxi and hot soak. There is still cooling when flying. The thermal expansion would fail the canister if the piston was solid. We need to confirm that as a fact.

I did some rough calculation using 40,000 psi yield strength, 4" dia, and .030" wall. Using longitudinal force due to pressure alone, 175 psi would yield 5100 psi. But - the spreading forces (hoop stress) from the threads would be a factor. It may have actually failed there first then progressed with a brittle failure around the circumference. Inspection of that broken piece may show low cycle fatigue there.

I don't believe (at this time) that the bending forces were sufficient to cause the failure.

Since this is a theory and hinges on hydraulic lock, then we need to know if that is possible. Either by test or analysis. I have 175 psi shop air. I will preload to 10 psi and pressurize the canister and compare the gages as pressure advances.

Meanwhile, I am happy to do the calculation for pressure vs location of the piston of the dimensions of the piston are provided. This is another way to understand what happened. The dimension between the end caps, the ID of the bore, length of the piston, and approx cavity size on both sides. I assume it is symmetrical. Also the dimensions of the end cap depression are needed. I can guess from the pictures, but numbers would be better.

To your question Des - I would NOT use this electric valve in this configuration. Just remove the valve and plump directly. This failure has nothing to do with an aircraft application.

Update - see my post and bought calculation below.
Cheers,
 
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Vibrations, metal fatigue, the lack of a pressure release valve that could have prevented hydraulic locking, mounted location, installation. Seems there are a lot of factors that have and could have contributed to this failure. Adopting some or all of these probably would have prevented this failure at this time. The system operated fine without the valve for over 3 years, with no signs of an issue when the valve was fitted in November 2016.
I'm really learning a lot through everyones posts. Would I fit the same system again and if I did how would I?

The thickness of the accusump wall concerns me, along with why the valve operates as it does. The pressure I read on the air valve at the bottom of the accusump which is up to 160psi after closing the valve and shutting down the engine. (Note this drops when the oil is cool and before I pre-oil the engine). I believe I was the first to fit this half raven system in NZ and it was all new to us RV guys in NZ, and I wanted to do aeros. The engineer who fitted it just fitted one a few weeks ago and now wants to remove it ASAP. Though he has not fitted the valve he is not happy with the thickness of the accusump.

There are many who are a lot more educated and experienced than myself and moving forward I believe an accusump is a good system, I just don't know if 0.8mm is enough strength to beat my life and engine on.

Looking for an answer and advice that others and myself can use.
 
According to scaled measurements off of the OP photos, combined with some measurements from my 1 qt accusump, assumed dimensions of the piston to be 1" long with an equal cavity to the end cap. Using P1V1=P2V2 , at 10 psi precharge, the piston will go SOLID at ~140 psi. All temperatures assumed the same. A lower precharge would go solid faster. (Edit: The oil side was pressurized with 180 psi shop air while reading then air side gage. The air side read 160+psi. The conclusion is it did not go solid up to 180 psi. It just shows assumptions are not good for decision making.)

Until better dimensions are available - I would conclude that this unit went into hydraulic lock, and thermal expansion of the oil (alone) resulted in overpressure and failed the canister.

The dimensions are probably off. The calculation is not.

It is highly inadvisable to use this electric valve considering its operation as a check valve. This probably happens as it is a poppet valve design. Poppet forces are a function of the pressure forces on each side of the valve. Bad design for this application.

I will leave my accusump in place and feel quite safe in its operation without a valve. YMMV. Challenges, updates, and discussion welcome.

Edit - I should add- this was not an operator, or installation error. The product information on that valve should have identified this potential failure mode.

Randy, if you have the valve, you may want to reconsider how it's "check valve" behavior can affect your failure modes. Just as a precaution.
 
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It is highly inadvisable to use this electric valve considering its operation as a check valve.

Assuming the user desires the ability to pre-oil, the valve should not hurt a thing given two conditions.

One is obvious...install a pressure relief valve!

Two would be installing the electric or manual line valve as an isolated component so its mass isn't supported by the canister. Maybe vibrating mass contributed to this failure, or maybe it didn't. Doesn't matter. It's poor practice because it's hard to predict.

I'm entirely with Bill for service as an accumulator supplying oil when inverted (or otherwise interrupting pumped oil supply). The system doesn't need the line valve, or a pressure relief valve. It's always open to the engine oil gallery, and max pressure can't exceed gallery pressure.
 
Assuming the user desires the ability to pre-oil, the valve should not hurt a thing given two conditions.

One is obvious...install a pressure relief valve!

Two would be installing the electric or manual line valve as an isolated component so its mass isn't supported by the canister. Maybe vibrating mass contributed to this failure, or maybe it didn't. Doesn't matter. It's poor practice because it's hard to predict.

I'm entirely with Bill for service as an accumulator supplying oil when inverted (or otherwise interrupting pumped oil supply). The system doesn't need the line valve, or a pressure relief valve. It's always open to the engine oil gallery, and max pressure can't exceed gallery pressure.

I don't like a pressure relief valve tied directly to the oil supply. YMMV. One might just increase the precharge pressure to avoid hydraulic lock, and get a real valve that blocks flow from both directions, then a pressure relief could be isolated. It could also be remotely located to spray on the belly. It's only 175 psi (nominally) anyway. A -3 hose can do that.
 
Thank you Bill. If the valve only let oil into the accusump and not out then that is the logical cause. Very scary, and shows what can go wrong with new components. I am still at a loss regarding the pressures measured on the valve at the bottom. If I new how the valve operated the installation would have been different, and a pressure release valve a must if the valve is fitted.

I am curious to what others think of the thickness of the accusump wall and whether this is a worry?

I am inclined to look at the Moroso accumulator if I am to fit one again, or another substitute. Does anyone know of other accusumps failing?
 
The Moroso unit is thicker, and has a burst pressure rating of 500 psi. If you want a heavy duty unit the rating goes up to 2,000psi. I have had no issues on my medium duty unit. The pressure gauge on mine is at 60 psi.
 
Nice Conversation with Canton Racing (accusump)

I sent a note to Canton Racing and got a call from a tech guy. He asked for me to convey the results of our conversation.

1. The valve does operate as a check valve when "closed"
2. The mounting bands must be located square with the end of the tube. They help retain the threaded end caps.
3. He believes that hydraulic lock occurred and was not relieved due to lack of a relief valve. He said some desert racers remove the relief valve and have this same failure. They removed them because they "leaked". He thinks they popped off regularly due to hydraulic lock and temps.
4. He volunteered that the valve should not be mounted rigidly to the end cap with a nipple. He suggested a hose (like DanH) He did not think it was the root cause, but seemed concerned about that.
5. They do not have a known burst pressure, but thought it was north of 250psi.
6. He was unaware that the piston might be able to bottom and still show excessive pressure on the air gage. In the discussion it seems the piston is maybe 2" wide.

That is the factual part of the discussion. I asked for a more definitive answer for a recharge pressure vs oil side pressure at which the piston either goes solid, or 175 psi oil side is reached. I also asked for a firm number for burst pressure. Regarding these, he said the owner was "retired" but active in the company and he would put these on the top of his list of discussion topics at his next opportunity.

If anyone can provide me with the dimensions of the piston, a more accurate prediction of the piston behavior will be calculated and posted. If you want this for larger than the 12" long unit, contact me via email and we can discuss the dimension needs.

Des - it appears that the thickness of that wall may, indeed, not provide burst margin that we are comfortable with. I wonder what the oil filter burst pressure is by comparison. (Tempest says 400+ psi)
 
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Thank you BILL for all that useful information. It is a very good insight to things that can go wrong without full knowledge and research. I'm hoping this can help others. Looking through the installation instruction manuals, and reading the feedback I can see how some simple assumptions and lack of information added to this event. Truely blessed to have it happen on the ground while shutting down.

I am still unsure as to why the 2 accusumps installations I know of (including mine) read a far higher PSI on the gauge than the oil pressure. Is it to do with the vertical mounting? Whoudl the release valve be blowing off often?

The mounting bands were square with the end of the tube adding a lot more strength, however I am worried about the thickness of the sump and how long it would have lasted even if the valve was fitted remotely and a release valve fitted?

Measuring the total wall thickness of the accusump tube there is 0.6mm difference from one side to the other. 2.55 where the unit let go, and 3.15mm where thickest. That brings the thinnest area where the thread let go at around 0.8mm Is that enough?

Cheers
 
I still don't understand either how you are reading such a high pressure. Mine is always equal to engine oil pressure, give or take no more than 5 Psi.
 
Different Valve Types and other thoughts.

A few more pieces of information. The OP and I are using different valves. He's using the Electric Valve - 24-270. I'm using the Electric Pressure Control Electric Valve - 24-275 - https://www.cantonracingproducts.com/product/24-275/24-275----ACCUSUMP-EPC-VALVE-55-60-PSI/

The two valves operate very differently. Unfortunately, their names are so close as to cause confusion. The standard Electric Valve, WITHOUT the Electric Pressure Control, like the OPs, restricts the accumulator refill flow rate. The Electric Valve is intended for pre-oiling and normal automotive street applications. It would be completely inadequate for my application - aerobatics - where the accumulator must discharge and refill quickly and often. If you want to use an accumulator in an airplane, I think you should either use a manual valve, no valve at all, or the Electric Pressure Control Electric Valve. These are all Canton Racing Product descriptions. Other manufactures may be different of course.

I do not have a check valve installed in my system. When the EPC has the valve closed, the accumulator will refill anytime engine pressure is above about 60 PSI. When pressure drops below about 55 PSI, the valve opens and the accumulator rapidly discharges to maintain engine oil pressure briefly. If by check valve, we are referring to the fact that, when the valve is closed, oil can only move into the accumulator, then I agree that is it's function. I don't see how that can be a problem though. It's operating as designed when it does that. One big advantage of the EPC Electric Valve is that, after discharge, as the engine oil pump is restoring pressure to the engine, it doesn't also try and refill the accumulator. The EPC Electric Valve won't let oil flow into the accumulator until engine oil pressure has recovered and is above the threshold.

I suspect the OP was seeing higher than engine operating pressure on the gauge (160PSI) after shutdown due to thermal expansion of the oil in the accumulator with the valve closed. This is one of the reasons I choose not to put the accumulator in the engine compartment. If you choose to put the accumulator in the engine compartment, I would advocate forgoing the pre-oiler function and allowing the accumulator to discharge completely on shutdown. This also makes checking the pre-load easier as you won't see engine pressure on the air side.

I like the idea of remotely locating the safety relief valve. Might have to look into that, especially as my accumulator is in the cockpit.
 
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I am not certain about how my electric valve works, but with it closed right after landing, and taxiing back to the hangar, I have never seen over 65 psi.
 
I am not certain about how my electric valve works, but with it closed right after landing, and taxiing back to the hangar, I have never seen over 65 psi.

And I don't think you normally would. I was suggesting that you might see a higher pressure as the oil in the accumulator heats up after shutdown or during extended ground operation. That still shouldn't be a problem in a properly serviced accumulator though. You're just compressing the air side. The problem comes when the temps rise, the air side is very low or empty, and the incompressible oil has nowhere to go. The safety relief valve would normally handle that situation.
 
Thank you everyone for your response to this. It has given me a good insight to the dangers of fitting something new in an aircraft and the need to get correct detailed information. We have had an RV with a full inverted oil system here in New Zealand overspeed a prop coming out of a spin, so I am intent on operating my RV with an accumulator for many reasons.

I have decided to fit the Moroso Heavy Duty Accumulator. The Heavy Duty 1.5Q Moroso has a tested burst pressure of 2000psi well beyond what is needed, however for just a few more dollars and very little extra weight I feel fully confident. After talking to a couple of engine rebuilders the pre-oiling system seems to be well worth it so I have opted for an electronic valve with a built-in pressure release of 35-40PSI. Talking directly to tech support I feel confident with this set up. They see no issue with mounting the valve directly on top of the Accumulator, however we will decide this when the unit arrives.

Below is what I have ordered. If you have any thoughts or comments please let me know.

Cheers

Desmond



Delete* Part # Description Quantity Unit price (USD) Total price (USD)
23903 Heavy Duty Accumulator, 1.5 quart capacity
Heavy Duty Accumulator, 1.5 quart capacity, 12" X 4-1/4" cylinderHeavy Duty Accumulator, 1.5 quart capacity, 12" X 4-1/4" cylinder

each 254.49 per each 254.49
23921 Accumulator Mount for Heavy Duty Style
Accumulator Mount for Heavy Duty Style No. 23902 and 23903Accumulator Mount for Heavy Duty Style No. 23902 and 23903

ST 32.94 per ST 32.94
23908 Electronic Pressure Control Accumulator Solenoid Valve
Electronic Pressure Control Accumulator Solenoid Valve, 12 volt, 35-40 PSI discharge and refill, Race/Street
ApplicationsElectronic Pressure Control Accumulator Solenoid Valve, 12 volt, 35-40 PSI discharge and refill, Race/Street
Applications

each
 
Revisiting this thread as I am plumbing a 3qt Accusump in my Rocket.

Analyzing this failure clearly points to the fault being not having the relief valve installed.

The problem with the supplied relief valve is it appears to be a air compressor relief valve that vents open. Venting overboard is not a good thing obviously.

I'm looking for a relief valve that has an AN fitting that I can run to a oil return port on the accessory case. I haven't found a suitable valve yet and am open to suggestions.
 
Revisiting this thread as I am plumbing a 3qt Accusump in my Rocket.

Analyzing this failure clearly points to the fault being not having the relief valve installed.

The problem with the supplied relief valve is it appears to be a air compressor relief valve that vents open. Venting overboard is not a good thing obviously.

I'm looking for a relief valve that has an AN fitting that I can run to a oil return port on the accessory case. I haven't found a suitable valve yet and am open to suggestions.

Have a look at a Sun Hydraulics RDBA/LSN valve, 12 gpm, 50-100 PSI relief range and ACI manifold SAE #6 ORB ports. I guessed at the flow rate and port size. If you need bigger, there should be lots of other valve to choose from. The relief valve should be direct acting not piloted.
https://www.sunhydraulics.com/model/RDBA/LSN
https://www.sunhydraulics.com/model/ACI
 
Revisiting this thread as I am plumbing a 3qt Accusump in my Rocket.

Analyzing this failure clearly points to the fault being not having the relief valve installed.

The problem with the supplied relief valve is it appears to be a air compressor relief valve that vents open. Venting overboard is not a good thing obviously.

I'm looking for a relief valve that has an AN fitting that I can run to a oil return port on the accessory case. I haven't found a suitable valve yet and am open to suggestions.

The issue in the OP was the valve did not shut off and acted like a check valve when off. It allowed the peak pressure to be attained then the physical expansion of the oil generated excessive pressure, repeatedly until failure of the cannister.

Are you using a cutoff valve? or just tied directly into the oil system?

To the question, I don't know personally of such a valve, but a Parker Hannifin 1/4" not valve is listed on eBay - -it is inline but currently set to 1800 psi, so a bit high.
 
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The issue in the OP was the valve did not shut off and acted like a check valve when off. It allowed the peak pressure to be attained then the physical expansion of the oil generated excessive pressure, repeatedly until failure of the cannister.

Are you using a cutoff valve? or just tied directly into the oil system?

To the question, I don't know personally of such a valve, but a Parker Hannifin 1/4" not valve is listed on eBay - -it is inline but currently set to 1800 psi, so a bit high.

That's part of the story here. It was plumbed to the oil cooler which is the point of highest pressure after the pump, which explains the higher pressures. I am just using a simple ball valve as the accumulator is mounted behind the baggage compartment for CG and room purposes. Don't anticipate any valve issues.

I've thought about mounting the relief valve inside a gutted inline fuel filter body, but I would like have a way to trip a limit switch so I can add an alert in my engine monitor if it bypasses. Hard to believe a discharging bypass valve doesn't exist for this sort of application. Household hot water heaters have had this sort of thing for decades.
 
Oh they exist, just not for this type of application. Most are known as backpressure maintenance valves, or priority valves, where they will hold a pressure on one side of the valve up to some maximum value, at which point it opens slightly and allows some of the fluid to pass to the lower pressure side, but continues to hold the set pressure against the high pressure side.

Here's a version used for high pressure air that I'm familiar with, 1/4" NPT fittings and adjustable up to 6000 psi. This particular unit is not suitable for the oil system as the minimum set pressure is too high, but you get the idea.

https://valvesandregulators.aquaenvironment.com/item/ard-flow-back-pressure-regulators-priority-valves-/1310-back-pressure-regulator/1310
 
If you'll call the guys at AquaEnvironment and ask to speak with one of their engineering team, you'll find them both competent and helpful for adapting their products to "out of the box" applications. I've done quite a bit of that.
 
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