fuel pump relief valve
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Join Date: Dec 2006
Location: Arkadelphia, Arkansas
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fuel pump relief valve
Just curious if anyone knew of what would happen if a relief valve on a O-320 were to develop a leak? I'm trying to gather up some info for a relative who owns an RV4 who experienced momentary power loss for 3-4 seconds with full tanks, 3000 MSL, straight and level. He's been experiencing lower than normal fuel pressure on startup (around 3 PSI) normally around 4-5 PSI, but it remains normal after startup. all engine instruments in the green. He returned to the airport circled overhead and tried to recreate the problem to get more info on the problem but he couldn't reproduce it. Any thoughts?
I realize this might better go in techlog, but i figured since this is afterall for a GA aircraft i may try here first.
I realize this might better go in techlog, but i figured since this is afterall for a GA aircraft i may try here first.
Last edited by bwicker; 27th Nov 2007 at 09:19.
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fuel systems
Some thoughts but sorry no solution.
If the engine was running at constant speed, as in straight and level flight, and the pressure relief valve had a constant leak it was obviously not leaking enough to affect the engine at that speed. It sounds as though something else is happening to cause a change in the steady state.
If the engine had run up on the ground developing max power then it would seem reasonable that there is sufficient fuel flow for this case too.
If the leak was not constant and caused by poor seating of the valve, or sticking when open then it may well open under a pressure surge and stay open. That would normally require a change of state in the fuel pump pressure to ocurr, or possibly the fuel itself.
I have had a similar problem with a car and a valve that intermittently would not seat properly. Once it appeared the engine would not rev beyond 2600rpm and the problem would not clear by restarting etc. apparently taking its own time. It occurred apparently randomly ie not related to engine speed, acceleration, declerration etc.
What about other causes ?
Ignition ?
Carb Ice ?
Accumulated water dislodged from a low point in the fuel tank/system ?
The fuel pump itself ?
If the engine was running at constant speed, as in straight and level flight, and the pressure relief valve had a constant leak it was obviously not leaking enough to affect the engine at that speed. It sounds as though something else is happening to cause a change in the steady state.
If the engine had run up on the ground developing max power then it would seem reasonable that there is sufficient fuel flow for this case too.
If the leak was not constant and caused by poor seating of the valve, or sticking when open then it may well open under a pressure surge and stay open. That would normally require a change of state in the fuel pump pressure to ocurr, or possibly the fuel itself.
I have had a similar problem with a car and a valve that intermittently would not seat properly. Once it appeared the engine would not rev beyond 2600rpm and the problem would not clear by restarting etc. apparently taking its own time. It occurred apparently randomly ie not related to engine speed, acceleration, declerration etc.
What about other causes ?
Ignition ?
Carb Ice ?
Accumulated water dislodged from a low point in the fuel tank/system ?
The fuel pump itself ?
Thread Starter
Join Date: Dec 2006
Location: Arkadelphia, Arkansas
Age: 39
Posts: 15
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'ppreciate all the responses; it's one of those problems where it could pretty much be anything :P So, we're just trying to tackle them one at a time ruling each one out! Total pain in the 
, but eventually we'll look back on it as a learning experience 
, but eventually we'll look back on it as a learning experience
