What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

How to pick up manifold pressure for the P-Mag

Tomas J

Active Member
I'm installing dual P-mag's in my RV-4 and thinking of the best way to get the manifold pressure. I'm thinking of installing a DISCHARGE NIPPLE AN4022-1 in cylinder #3 or #4 primer port, and use a AN FITTINGS AN824-2D TEE to split the pressure for both ignitions. Or is it better to give the ignitions manifold pressure from separate cylinders, use both #3 and #4 and skip the tee?

But what about the fluctuates in pressure? Will they affect the ignitions? Can the discharge decrease that effect? Is there an alternative and better place to get manifold pressure on a Lycoming 320 with Marvel carburator?
 
Tomas----we pull MAP from cylinder 3, route the hose (generally a -3 hose) to a dual tee for the PMags and the MAP sensor. -3 hose because the stem ID is .079 and 'generally" doesnt need a restrictor fitting for the EFIS MAP readings.
Flying on alot of different experimentals.

Tom
 
I have an O-320 on my -9A. I used a -3 line off #4 cylinder into a precision needle valve screwed into the standard Van's manifold block on the firewall. The output from the block goes to a brass tee fitting to split the tubing going to the dual Pmags. The purpose of the needle valve is to provide a variable orifice to smooth out the pulses going to the Pmags. Before installing it on the manifold I blew through the valve and set it to only let a small amount of air through. Not very scientific, but I was concerned taking the vacuum signal right behind one intake valve would send strong pulses to the Pmag which would confuse it. I wish Lycoming provided a vacuum port on the intake manifold that would automatically combine and average intake pulses. I wish I had machined one in when I built the engine...
 
pUT A "t" IN THE LINE FROM YOUR MANIFOLD PRESSURE GAUGE OR TRANSDUCER, THEN TO BOTH P MAGS. GIVING THEM THEIR OWN MP FROM SEPARATE CYLINDERS HAS CAUSED ISSUES WITH TIMING FLUCTUATION. rEGARDS,

dar GARY
 
Tomas,
Like Tom, I had a fitting off cylinder 3 with #3 braided line (TS Flightlines), going to a T fitting on the firewall, which supplied the MAP line, and the dual Pmags. My fitting on the #3 cylinder was a steel restrictor fitting, although I don’t know if that was necessary. I used small aluminum lines with flared fittings for much of this (I think it was 1/4”, but not sure), but when it got near the Pmags, I transitioned to the silicone tube supplied with the Pmag kit. I used a nylon barbed fitting with a clamp to split the pressure source on that silicone line to the two Pmags.
It worked well for my with no noticeable fluctuations.
 
Here’s a pic of my install. Braided line to an AN fitting/aluminum line - to a T (blue on the firewall manifold), feeding the MAP sense probe, and also to the Pmags. The nylon T in the silicone line to the two Pmags isn’t visible.


8C13E456-F573-4857-8D8A-259EC0A15C13.jpg
 
A simple brass fitting to replace the manifold plug (pipe thread) with 1/8" barb, and use 1/8" vacuum line from auto parts. The "T" can be as simple as a "T" from the irrigation section of ACE hardware or any hardware store.

CHEAP.....SIMPLE.....AND LIGHT.
 
Mickey and others, using the brass tee is fine if you use a 306 rubber hose from the cylinder. It doesnt work with teflon, 1 because of the OD/ID differences, and 2 because of the stiffness of the teflon liner, it doesnt seal well with barbs. Rubber does give, expands and then contracts and seals the gap in the barb between the root and the peak. Teflon, being stiff, doesnt collapse to fill the void.

Since most of our clients doing this install are using teflon, we came up with this dual tee for 2 PMags/Sureflys. Can be done alot of different ways, but the object lessen is to NOT have a MP leak which creates other issues.

Tom
 

Attachments

  • RV7A DUAL PMAG TEE.jpg
    RV7A DUAL PMAG TEE.jpg
    681.3 KB · Views: 790
... Since most of our clients doing this install are using teflon, we came up with this dual tee for 2 PMags/Sureflys. Can be done alot of different ways, but the object lessen is to NOT have a MP leak which creates other issues. ...
Tom, this is a nice solution and looks very solid. Your kit would have saved me a lot of time and money buying bits that didn't work. :)
 
Tom, it looks like a tee on the manifold would let you run a line from the cylinder to the manifold, then connect the Pmags to that tee. If this is feasible, it would save you the weight and volume of one tee and the connection to the other. It would also let you eliminate one plug on the manifold.

I am building an RV-3B, and there's not much room in that area.
Thanks,
Dave
 
Last edited:
Tomas,
Like Tom, I had a fitting off cylinder 3 with #3 braided line (TS Flightlines), going to a T fitting on the firewall, which supplied the MAP line, and the dual Pmags. My fitting on the #3 cylinder was a steel restrictor fitting, although I don’t know if that was necessary. I used small aluminum lines with flared fittings for much of this (I think it was 1/4”, but not sure), but when it got near the Pmags, I transitioned to the silicone tube supplied with the Pmag kit. I used a nylon barbed fitting with a clamp to split the pressure source on that silicone line to the two Pmags.
It worked well for my with no noticeable fluctuations.

I installed dual Pmags on my 0-320 and followed the instructions using separate sources for the MAP lines. What's this talk about fluctuations? Is this something to be concerned about? If a restrictor fitting was required wouldn't that be in the instructions? In over 20 hours of operation since installation, I have no issues that I am aware of.
george
 
Update

A builder friend just got his Pmags and they included a little fitting for the vacuum line with a restriction built in. I do not know the size of the restriction, but it was noticeably smaller than the fitting ID. It looks like the Pmag guys figured out a simple solution to the pulse issue.
 
David----to run dual pmags and the map sensor, you need 4 ports. Spruce has a really nice aluminum manifold with 3 ports, or 5 ports like the pic. You still need the AN fittings to complete the install. WE felt like ours was simple, and relatively inexpensive.

Mickey--sorry man. WE try to listen to what guys are asking for, and sometimes we announce it, and sometimes not.

Ya'll have ideas? What the heck, Steve and I will take a crack at it.

Tom
 

Attachments

  • 04-00102 Spruce manifold.jpg
    04-00102 Spruce manifold.jpg
    17.6 KB · Views: 149
Answer from E-Mag

Thanks all for reply. I wrote a question to E-Mag and got this clarifying answer from Brad...
"If you have existing manifold plumbing, it’s best to fashion a tee into an existing line. If not, it’s common to use the primer port (1/8” NPT) if you are installing on a Lycoming. Picking up closer to the carburetor is a cleaner signal but we include a pulse dampener so it’s not a significant issue. Alternatively, an orifice can restrict pulses and can serve to minimize air imbalance in the event of a plumbing failure. On normally aspirated engines, our MAP input is fail-safe so ignition firing will remain serviceable in such event."
 
David---after sleeping on this, I assume you are speaking of the tranducer manifold on the firewall. So yes you can use a AN825 or AN826, probably the 826 to plumb this.

Tom
 
Tom, that's what I was thinking. I was trying to imagine what I was missing after reading your previous post - thanks!

Dave
 
AN826

Tom, that's what I was thinking. I was trying to imagine what I was missing after reading your previous post - thanks!

Dave

The AN826 will supply MP to two P-mags but what about MP to the EMS?
Don't you still need another "T" somewhere?
 
Does anyone have a source for the fitting that fits to the AN826 fitting and small enough for the 1/8" hose to the PMAG?
 
My solution ( on all four dual P-Mag airplanes in our hangar) is to put a pneumatic QD nipple into the extra MAP hole on the Van’s sensor manifold on the firewall, then run a piece of tubing to a “Y” pneumatic QD, then then a single lien from the “Y” to each P-Mag. Works great, and you can disconnect very quickly at the input to time both P-Mags with the same breath puff.

The tubing that comes with the P-Mags fits perfectly into the 1/4” pneumatic QD’s....

Paul
 
My solution ( on all four dual P-Mag airplanes in our hangar) is to put a pneumatic QD nipple into the extra MAP hole on the Van’s sensor manifold on the firewall, then run a piece of tubing to a “Y” pneumatic QD, then then a single lien from the “Y” to each P-Mag. Works great, and you can disconnect very quickly at the input to time both P-Mags with the same breath puff.

The tubing that comes with the P-Mags fits perfectly into the 1/4” pneumatic QD’s....

Paul

That works for me too.... . When following the thread I was wondering why people think this is so complicated.... .

Oliver
 
Merhad---with the AN826-3D tee we use our -3 hose end fitting stem and nut with out the crimp collar. With the AN826-4D tee, we wuse our -4 nut, -3 ste and body jump size hose end stem with out the collar. Fits the PMags supplied silicone hose fine.

Tom
 
Single pmag fitting

I have a single pmag. Does anyone have a suggestion for a straight fitting for the #3 MAP port to the pmag supplied tube? Can't seem to find one.

Thanks
 
I read this thread having just modified the MAP fitting on my RV-14A for dual p-mags, but I think my solution should work. What I did was replace the F-4 DTX-S on the Garmin firewall-mounted transducer with a 4-MTX-3 tee and 4-G6X-S adapter to 1/4" NPT where I connected a 90 deg 1/4" pneumatic swivel fitting. I ran 1/4" tubing to an insert tee then ran the rubber tubing supplied by E-Mag to each p-mag with the supplied pulse dampener in each line. On the RV-14A, the manifold pressure is taken off the #3 cylinder with a braided hose supplied by Vans which connects to the other side of the 4-MTX-3 tee.
 

Attachments

  • IMG_8625.jpg
    IMG_8625.jpg
    221.1 KB · Views: 262
No tee's please

I read this thread having just modified the MAP fitting on my RV-14A for dual p-mags, but I think my solution should work. What I did was replace the F-4 DTX-S on the Garmin firewall-mounted transducer with a 4-MTX-3 tee and 4-G6X-S adapter to 1/4" NPT where I connected a 90 deg 1/4" pneumatic swivel fitting. I ran 1/4" tubing to an insert tee then ran the rubber tubing supplied by E-Mag to each p-mag with the supplied pulse dampener in each line. On the RV-14A, the manifold pressure is taken off the #3 cylinder with a braided hose supplied by Vans which connects to the other side of the 4-MTX-3 tee.

Hi Marty
I'm just looking for a straight out connection from the MAP port on cyl 3. No Tee's, just direct to the Pmag. Looks like a brake fitting might work but couldn't find a straight fitting, just 90s and thre is no room to turn the fitting due to interference.

Thanks.
 
Michael---you and use a AN816-3 or 4 fitting---depending on the size of hose you are planning on using for the tee to the PMag and the MAP sensor. WE generally use -3 . AND the location of the MAP sensor plans into this.

BUT---in your case, a straight AN816 fitting to the PMag barbed fitting with a 1/8 ID Hose. If the hose that PMag supplies is long enough, you can use that.

Tom
 
The tube connection

Michael---you and use a AN816-3 or 4 fitting---depending on the size of hose you are planning on using for the tee to the PMag and the MAP sensor. WE generally use -3 . AND the location of the MAP sensor plans into this.

BUT---in your case, a straight AN816 fitting to the PMag barbed fitting with a 1/8 ID Hose. If the hose that PMag supplies is long enough, you can use that.

Tom

Hi Tom
I do have spare AN816 (probably from one of the other kits you sent me) but didn't think you could use the flare side to hold silicon tube. Is that ok ? Pardon my ignorance.

Michael
 
"to the PMag barbed fitting with a 1/8 ID Hose. If the hose that PMag supplies is long enough, you can use that."

So if the Pmag has a 1/8" barbed fitting, then just go to the hardware store and get a 1/8" brass NPT to 1/8 barbed..... https://www.amazon.com/FasParts-Straight-Brass-Fitting-Water/dp/B013RYN3OA This fitting has been used in the automotive industry for over 100 years. And vacuum hose from NAPA auto parts will be equal or better quality replacement for the Pmag hose.

Here is the item except you need 1/8 X 1/8...... https://www.aircraftspruce.com/catalog/hapages/15-06132.php You can get this at any hardware store.

No reason to not keep it simple and lite.
 
Last edited:
Perfect

"to the PMag barbed fitting with a 1/8 ID Hose. If the hose that PMag supplies is long enough, you can use that."

So if the Pmag has a 1/8" barbed fitting, then just go to the hardware store and get a 1/8" brass NPT to 1/8 barbed..... https://www.amazon.com/FasParts-Straight-Brass-Fitting-Water/dp/B013RYN3OA This fitting has been used in the automotive industry for over 100 years. And vacuum hose from NAPA auto parts will be equal or better quality replacement for the Pmag hose.

No reason to not keep it simple and lite.

That’ll do it. Thanks
 
Back
Top