smoke system question

Christopher Murphy · #1 05-14-2009, 11:09 AM

I built my own system that uses a pump with a pressure shut off at 70psi. The system works great for about 10seconds until the press builds up and then the pump starts cycling on and off. ( Pretty white dashes in the sky)

I am considering two fixes.
1) install a "accumulator" in the pressure line ( maybe made out of 1 inch dia. pvc with caps and hose barbs to install in the hose line.)
2) Install a "T" fitting in the line and run a return line back to the tank.

This first option would be easier...what do you engineer types think?

Chris Murphy RV-4

Mike S · #2 05-14-2009, 11:18 AM

Is the pump pressure regulator adjustable????

You could open up the nozzle a bit, but that would give you less total time "on smoke".

Good luck.

Dave Cole · #3 05-14-2009, 11:28 AM

Install a tee in the pressure line from the pump and insall a small adjustable flow control in the branch of the tee with a return line back to the tank. You can use the flow control to adjust the amount of oil that will flow back to the tank, and the rest will flow through your oil injection orifice. The pump will run continuously as long as the switch is on.

Veetail88 · #4 05-14-2009, 11:33 AM

If you run a return line, you'll need a valve in the line that will hold position so you can throttle the flow I would think.

As the pump motor is DC, couldn't you slow down the pump with a resistor or rheostat in the line? You may be able to match the pump output to the nozzle oriface that way.

An accumulator would have to be some type of bladder type of vessle and would need to be pretty large to absorb the extra flow from the pump to solve your problem that way. Then, when you turn the pump off, the oil would have to be able to flow back through the system. I don't think that would be a very good option.

You could also try restricting the flow on the suction side of the pump, but the pump may not like that very much depending on it's design.

frankh · #5 05-14-2009, 11:57 AM

The ideal would be a pressure sustaining valve in a return line going back to the tank...This is how you get constant pressure with a varying demand..Indeed this is how the AFP pump system provides canstant pressure to the back of the mechanical fuel pump..but I digress.

In this case you have a constant load bacause you have a fixed orifice size at your point of injection..So really all you need is a return line with a fixed orifice size to keep the pressure constant at the injection nozzle...What your really doing is feeding two nozzles that flow the total output of the pump at a certain pressure..You want that second orifice the right size to make that pressure..maybe a brass plug in the end of the tube that you gradually drill a hole through, then gradually increase out tothe size to get you the required pressure.

Why does the pump take 10 seconds to come up to pressure?..seems a long time!

Frank

Christopher Murphy · #6 05-14-2009, 12:09 PM

Quote:

Originally Posted by frankh

The ideal would be a pressure sustaining valve in a return line going back to the tank...This is how you get constant pressure with a varying demand..Indeed this is how the AFP pump system provides canstant pressure to the back of the mechanical fuel pump..but I digress.

In this case you have a constant load bacause you have a fixed orifice size at your point of injection..So really all you need is a return line with a fixed orifice size to keep the pressure constant at the injection nozzle...What your really doing is feeding two nozzles that flow the total output of the pump at a certain pressure..You want that second orifice the right size to make that pressure..maybe a brass plug in the end of the tube that you gradually drill a hole through, then gradually increase out tothe size to get you the required pressure.

Why does the pump take 10 seconds to come up to pressure?..seems a long time!

Frank

I think it just takes that long for the press to exceed the shut off limit. ( open syst at the injectors). I cant find any info on the the press switch to see if it is adjustable. I think the pump is way too big for this job but it was recommended. Before I start adding to the syst I have a facet fuel pump I will try. About the accumulator... I don't care if the pump cycles I just need a continues flow at the nozzle so I thought adding volume in the press line would dampen out the pressure cycles.???

I think the best thing to do is a return line but I wanted to keep it simple...ha!

frankh · #7 05-14-2009, 12:37 PM

I mean think about it you have an accumulator and your doing aerobatics..as soon as you go negative you'll fill the system with air and you've lost your accumulator anyway..

I'd try the Facet first as they are internally relieved..Migth be the simplest option if it has enough oopmh..Technical engineering term..

Kahuna · #8 05-14-2009, 12:53 PM

Is this a 'demand pump', like for a boat? Designed to jump on and off (on demand)when the pressure drops?

Christopher Murphy · #9 05-14-2009, 01:05 PM

Yes it is a demand pump. I guess because of the size of the orifice in the nozzles it builds up enough press to shut off. I am going to try the facet pump and if that is not sufficient I will install a return line of somekind and use the bigger pump. I makes good smoke when it runs so its just a matter of refinement.

Chris M.

ps. Who ever mentioned negative manuevers.... not a factor... no inverted syst.

jthocker · #10 05-14-2009, 03:41 PM

Chris,
I'm having the same issue with my pump. I installed a needle valve in line from the pump to the nozzle, so as to meter the flow. I was hoping to get some of the unburned oil off the belly, but when I restrict the flow my pump now cycles and it looks like I'm sending morse code via smoke. I think my fix now will be to install a second nozzle and try to burn it up that way.
I kind of feel like I'm doing my part to stimulate the economy by blowing thru a ton of smoke oil!