Author Topic: pressure carb??????  (Read 8645 times)

391stol

pressure carb??????
« on: January 15, 2011, 06:08:54 PM »
How come helio used the ps-5 pressure carb instead of of a ma4-5 or injection?  I realize the lack of carb ice compared to the pressure carb or injection. Can a standard updraft carb be installed in place of the pressure carb? Injection is to costly.

mrhelio

  • Guest
Re: pressure carb??????
« Reply #1 on: January 16, 2011, 07:19:22 AM »
In regard to the PS-5C Carburetor.  There is not a thing wrong with them.  They ARE different when compared to float carburetors, however.  They require fuel pressure in order to work.  They will work regardless of the attitude, and do not typically suffer from carburetor ice.  All the Cessna L-19's are equipped with the PS-5C carburetor, and there are several hundred still flying, and flying fine I might add.  It is a rather complicated beast when compared to a float carb, but quite reliable.  Just my 2c worth.

391stol

Re: pressure carb??????
« Reply #2 on: January 16, 2011, 05:19:27 PM »
WHy did Helio choose the pressure carb????? Seems to be many more float type carb. planes in operation than the pressure carb, must be some reason for that?? I am not knocking the pressure carb just wondering why it is not very popular or if has any advantage over the standard carb on the helio?? Not to mention the cost of rebuild parts.

45°

Re: pressure carb??????
« Reply #3 on: January 16, 2011, 07:14:33 PM »
Actually it was Lycoming that selected pressure carbs (just look in your Lycoming manuals) for use with the GO series engines, not Helio although it would make sense with the design goals of Helio at the the time to be as simple to operate as possible for the pilot... the pressure carb provides automatic altitude mixture control and enhanced cooling with a more efficient power enrichment circuit than most float type carbs for better cylinder cooling at full throttle which was likely Lycoming's main reason for selecting them. These are great carbs both in function and reliability, yes they are more expensive to overhaul and also require a 337 at overhaul as any pressure carb is considered a major repair at overhaul and one should not defer maintenance as one might on a float carbs.

mrhelio

  • Guest
Re: pressure carb??????
« Reply #4 on: January 17, 2011, 08:57:35 PM »
In response to the above post, it will also be interesting to note that the "pressure carbs" were initially designed for use in the Twin Bonanza and Aero Commander. Lycoming developed these for high speed and moderate altitude ops. Most normally aspirated aircraft with geared engine technology brought to you by Lyc. had Bendix design the carb. There are plenty of them, and can be had for reasonable prices as long as they have been "green tagged" and bench tested.

Ray Dorsey

Re: pressure carb??????
« Reply #5 on: January 26, 2011, 12:49:26 AM »
You Have source? Always looking for spares.
There is a nice little Bendix PS series manual that is available .  When the carb is adj.
per conditions. it works better then a float carb ,better mileage per conditions.

Ray

Doug Johnson

Re: pressure carb??????
« Reply #6 on: May 03, 2014, 09:05:23 AM »
Does anyone use the search feature and look for info on this site?

I still believe that converting to a Bendix fuel injection system is the way to go but....

I found a short article on pressure carbs while looking for lycoming info and thought I would post it here for anyone interested. Since it explains the pressure carb so well and points out a couple of important things.

Also Gordon Cragg probably has some advice on rebuilding carburetors hopefully he will share it.

The one that caught my attention was the pressure parameters for the carb I thought there was a broader range.

The second was that if you have never had the newer diaphragms installed it probably wouldn't be a bad idea.

So you've got a Bendix Pressure Carburetor....

This article was found on the Aero Commander Website (www.aerocommander.com). Following these guidelines will insure a long and peaceful life with the PS5-BD. Especially follow the rule about putting the mixture in “park” when the engine is not running. Many thanks to Chris for the most useful information.
© Chris Schuermann - 1996

If you own an airplane built in the 40's or 50's you just might also be the owner of one of
aviation’s most bizarre pieces of hardware - the Stromberg (Bendix) pressure carburetor.
This little marvel of engineering is the predecessor of fuel injection. Although technically
classified as a carburetor, it has no float system, and meters pressurized fuel much like a
throttle-body injection system.

The PS5 series carburetor can operate installed at any angle, and may even be used on
turbo-supercharged engines. I have heard that it is even possible that it may have been
configured for a "blow through" system although I can't find any literature on that
application.

Some interesting notes

The Bendix pressure carburetor has several unique traits.
It has an airflow-operated auto-enrichment valve, which provides an extra rich setting at
full power. It is important to maintain full throttle during the initial climbout using this
carburetor. A reduction in throttle will cause higher EGT/CHT than desired because the
carburetor is designed to provide an optimum lean mixture except at full throttle.
Many models have an automatic mixture control. The mixture knob is left in the full rich
position for all flight operations. A nitrogen-filled bellows assembly automatically
compensates for both altitude and temperature!

Complex too!

I've yet to see any carburetor as complicated as a pressure carburetor. It has more little
chambers, diaphragms, and passageways, etc. than would seem reasonable. That
noted, they run remarkably well when in good condition. They are also quite reliable
once rebuilt with the new synthetic diaphragms.

To tell if you have the new diaphragms, look at the edges of many pieces of the
carburetor. If you see what looks like black rubber gaskets, you have the older rubber
diaphragms. If you see orange, then you have the new synthetic ones.

Don't leave the mixture at idle cutoff!

A pressure carburetor needs to have the mixture control placed at the "park" position
after shutdown. If left in the "idle cutoff" position for any length of time, the diaphragms
will be damaged!

 (Ed. note: After speaking to Mike’s Metering Service, below, the mixture
can be left in ANY position after shut down as long as the new ‘orange’ diaphragms are
installed.)


Fuel pressure is also critical for a pressure carburetor. Most are set at 14 psi ± 1 psi.
Outside of this range the carburetor will fail to meter correctly.

If you get more than a 10 RPM rise during shutdown, the carburetor needs to go to a
shop. Also, if your bird isn't VERY easy to start, get the carburetor to a shop. My
experience is that engines with a Bendix carburetor should be VERY easy to start - hot or
cold. A very slight problem with the carburetor will cause hard starting.

There are only two principal adjustments that may be made without a flow bench: the
metered fuel pressure, idle mixture and idle speed. Don't mess with ANYTHING on
this carburetor if you don't know what you're doing. Turning almost anything affects
something else....

If you'd like a reference for a pressure carburetor guru who really knows his way around a
PS-series carburetor, feel free to drop me a note. A PS5BD carburetor exchange is
about $1200 ($1600 now!). The diaphragm kit is VERY expensive, and it takes a lot of
time to properly set one up on a flow bench...
Chris

PS- The reference Chris mentions above is:
Mikes A/C Fuel Metering Service, Inc. ($60/hr)
9406 E. 46th Street North
Tulsa, OK 74117
(918) 838-6217
(918) 838-7047 fax

or

PRECISION AIRMOTIVE ($75/hr)
3220-100th Street, SW #E
Everett, WA 98204
(360) 651-8282
(425) 347-2800 Manuals
Doug

Gordon Cragg

Re: pressure carb??????
« Reply #7 on: May 04, 2014, 09:16:43 PM »
If anyone has an issue with a Bendix pressure carb, I highy recommend Mike's Fuel in Tulsa. They are very accurate in troubleshooting and are very fairly priced.
They have overhauled and or modified 3 carbs for me and they have all worked as represented.
Gordon Cragg
713-502-7274