lml@lancaironline.net Mailing List Archive

Re: Continuous running hydraulic pump

Jeff,

I believe the “erratic” flap operation is caused by a slight “overlap” of the ports in the hydraulic flap valve. This basically allows fluid under pressure to go where it’s not intended. I have also noted that an intermediate position of the flap lever allows hydraulic fluid to pass directly from the high to the low side of the system, keeping it from pressurizing and also allowing the hydraulic pump to run continuously. I have annunciators to advise when the pump is running, and when the system pressure falls below 600 PSI (about the pressure needed to keep the gear fully retracted) These are good indicators that something is amiss with the system.

My IV-P hydraulic system used to leak down in 10 minutes or so during flight, causing the pump to activate momentarily, and to leak down to zero overnight. Clark Still suggested I put the flap valve in the off position when the flaps were not being used, and this completely stopped the pump cycling. My system will now hold pressure for at least a week on the ground. My conclusion is that I have an internal leak between the high and low side of the flap actuator (across the piston to be specific) I suppose it could be an internal leak in the flap valve, but the actuator cylinder is the more likely candidate for several reasons… I may try to rebuild it someday, but for now, the simple expedient of putting the flap lever in the off position works well!

If you must have it “fixed,” look first to the hydraulic flap actuator cylinder. You can test this by disconnecting the actuator from the hydraulic system, plugging the ends of the actuator lines and running a test by moving the flap valve under pressure. If you get no leak down/cycling with the cylinder removed from the system, it indicates the cylinder internal seal.

Bob

More observation:

If I leave my flap lever in the neutral position, the hydralic reservoir remains fully pressurized, and next time I fly there's no need for the pump to come on during power up to recharge the system.

I understand that some planes/pilots must leave their flap lever in the UP position, or the DOWN position to retain hydralic pressure until the next flight. If I did this, all pressure would be released. Why the difference with what is the same valve?

I also have seen the flaps move (briefly) in the opposite direction if lever is positioned just slightly off of neutral, during routine operations; I agree that this is a quirk in the internal valve.

Jeff Liegner

LIVP

This is case of creating a problem that wasn't there. My experience might ease someone's tension in the future.

While practicing an approach I got a "check engine" from the Chelton. The indication was low voltage. I quickly saw the hydraulic pump was running continuously. I pulled the hydraulic pump breaker. I got a "gear transition" light so I suspected no hydraulic pressure which was confirmed when I looked at the gauge.

I figured the best thing to do was to leave everything as it was and hand pump the gear down and land. This worked just fine.

Now the problem was that for the first time in over 600 hours of flying this thing, when I had set the flaps at 10 degrees I had left the flap handle a little out of the detent and the valve was just dumping the high side pressure to the low side and just kept the hydraulic pump running.

Some days I think that if every thing is going well I just create a problem for the practice. At least my rebuild of the gear hand pump worked well.

Dan Reagan

IVP 650 hours