Manifold pressure line filter

vanzed · #1 03-28-2007, 07:51 AM

The filter/orifice on my Vision Microsystems manifold pressure sensor blocked as well as there being grunge in the MP line to the Laser ignition advance. Can anyone point me to a filter that would be suitable to install in the line to the inlet manifold. Have looked in the usual catalogs and searched here to no avail. My contribution is that carburettor cleaner fixes the problem as well as removing locktite
Denis Vanzella
New RV6 owner

flybynight · #2 03-28-2007, 01:25 PM

I erratic readings on the MP guage on my Dynon EMS10 and cured this by putting a 'roll your own' cigarette filter in the line near the MP sensor. This cured that problem. This might work for you.
Tom Storey
RV9 G-CDXT flying

Bob Martin · #3 03-28-2007, 02:05 PM

Guys, I'm a backyard gear head, but MAP is vacuum and I wouldn't think you would want to install any kind of filter in the line, least you reduce the pressure readings. I will defer to more experianced people on this one, but be aware of inacurate readings with a filter.
I just installed Vans MAP kit and it takes it line from the bottom of #3 cylinder, the line goes down then back up to the firewall, maybe the low loop holds the crud.
My -6 had a 1/8 copper line from the top of #2 cylinder then back to the baffeling behind #4 to connect to JPI's MAP sender. The plane has 500+ hours and I didn't see any crud when I took the system apart.
good luck

airguy · #4 03-28-2007, 03:31 PM

Quote:

Originally Posted by Bob Martin

Guys, I'm a backyard gear head, but MAP is vacuum and I wouldn't think you would want to install any kind of filter in the line, least you reduce the pressure readings. I will defer to more experianced people on this one, but be aware of inacurate readings with a filter.
I just installed Vans MAP kit and it takes it line from the bottom of #3 cylinder, the line goes down then back up to the firewall, maybe the low loop holds the crud.
My -6 had a 1/8 copper line from the top of #2 cylinder then back to the baffeling behind #4 to connect to JPI's MAP sender. The plane has 500+ hours and I didn't see any crud when I took the system apart.
good luck

You're only going to get a pressure differential across a filter if you have flow in the line. Vacuum or pressure, doesn't matter, if the flow rate is at or near zero (which it is in this case) then the pressure will equalize in a second or two and that's it. A very restrictive filter in a MP gauge line will simply "smear out" MP changes due to a throttle change. A fast throttle movement may appear to be stretched out over 3 or 4 seconds on the gauge, but that's it.

As long as any EI or FI manifold pressure sensors are on the manifold side of the filter, or the volume of the line between the filter and the sensor is very small, you're golden. If you're trying to filter a sensor, then put them as close together on the line as possible - minimize the amount of dead volume between the filter and the sensor in the plumbing - preferably zero.

vanzed · #5 03-28-2007, 04:17 PM

Thanks
The "rolly" cig filter looks good we were actually thinking of one of those womens things, the former is probably more PC as well as being better suited to the task

Denis Vanzella

zilik · #6 03-28-2007, 04:25 PM

I used a cheap see through plastic fuel filter in this line. I replace it after 500 hours as a precaution but did not really have too.

AlexPeterson · #7 03-28-2007, 05:16 PM

What purpose does a filter in this line serve?

az_gila · #8 03-28-2007, 08:49 PM

Quote:

Originally Posted by zilik

I used a cheap see through plastic fuel filter in this line. I replace it after 500 hours as a precaution but did not really have too.

The sailplane guys also use the same type of filter Gary mentions....

While it is sold here....

http://www.cumulus-soaring.com/ilec.htm

I believe it is the same type you can get at your favorite auto parts store...

The pressure changes measured by the glider instruments are way less than that of a MP gauge and a fast instrument response is required, so this type of filter won't affect gauge operation...

gil in Tucson

flybynight · #9 03-29-2007, 01:50 PM

Quote:

Originally Posted by AlexPeterson

What purpose does a filter in this line serve?

My Dynon EMS D10 original gave a steady reading on the pictorial MAP guage but the attached digital read out was all over the place - not surprising as it is sampling the No3 cylinder many times per second. The cigarette filter smoothed the digital read out well.
Tom Storey
RV9 G-CDXT

gmcjetpilot · #10 03-29-2007, 01:59 PM

Quote:

Originally Posted by AlexPeterson

What purpose does a filter in this line serve?

I had massive problems with my RV-4 and a old fashion mechanical MP gauge. The gauge got contaminated with an oily gas mixture, which migrated down the hose. My solution was two fold, A restrictor fitting and a service loop so to speak.

Originally, I had an AN fitting in #3, hose and fitting in firewall and a hose to gauge. The hose pretty much went straight from Cyl to firewall. All fittings where standard AN fittings.

First, I modified the AN fitting with restrictor plugs on both the cylinder and firewall AN fittings. I made them with a rivet and a small 1/32"-1/16" hole drilled in it. The reduced orifice had no affect on the gauge.

The 2nd part was to extend the hose and make a service loop. After leaving the #3 cylinder intake port, I used a longer flex hose that went down towards the bottom of the firewall to a Tee fitting held in a bracket. One leg of the Tee was capped, the other leg went up to the original firewall to cockpit fitting, using a ridged aluminum tube. I would open the cap on the Tee and drain a few drops of mosture/gas/oil mixture every once and a while. problem solved.

Doing both restrictor fittings and hose re-route at the same time its hard to say what did the trick. However I got very little liquid in the hose/service trap. Doing it over I'd just go with a longer hose with a good elevation drop/loop or dip. Make sure the MP fitting is high in the firewall. Probably a good idea to clean out the lines on occasion, which should take a few minutes.

I think a restrictor fitting on the Cylinder is the first line of defense. Clearly its in the intake port area where there is fuel/air mixture. It only makes sense some will find its way into the hose. The restrictor and the LOW POINT in hose method works well, with out a filter.

This fuel in the MP gauge is not an uncommon problem, I had a factory plane blow gas into a MP gauge.

Filters? I think its not needed and might cause problems. Looks like the one above is for pitot/static. Not against it or saying it would not work, just I like to keep it simple. The restrictor and loop/dip is good enough for me. However YOU have should clean the hose out on occasion, just like a filter, if that is the way you want to go.