meister808
Posts: 924
Joined: Sat Jan 01, 2000 11:45 am

Seneca PA34-200T Landing Gear Question

Thu Aug 14, 2008 5:50 am

Quick question, not sure how many light airplane guys we have out there, but I figured this is driving me up a damn wall and here might be a good place to get an answer.

What turns off the landing gear pump in a Piper Seneca II (1978 PA34-200T) on retraction? I'm close to 100% sure that 3 closed down-lock switches turn off the pump when the selector handle is in the 'DOWN' position, but for the life of me I cannot seem to track down what turns off the pump in the 'UP' position.

The POH says in flowy imprecise language, that 'limit switches' turn the pump off once the gear is fully extended or retracted. This would lead me to believe that 3 closed up-limit switches turn the pump off.

HOWEVER, there's a pressure switch shown on the landing gear schematic and on the landing gear electrical diagram. It isn't mentioned anywhere in the text of the system description, but I seriously doubt that Piper installed a completely useless pressure switch on the gear system. Does this pressure switch turn off the gear pump when the handle is in the up position, a la later Piper products such as the Arrow and Seminole, or is the pressure switch some sort of overpressure cutout... I'm moderately confused.

Anybody got ideas?

-Meister
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
 
lowrider
Posts: 2542
Joined: Wed Jun 30, 2004 3:09 am

RE: Seneca PA34-200T Landing Gear Question

Thu Aug 14, 2008 6:34 am

If I recall correctly(and it has been a while), the pressure switch will cycle the pump on to hold the gear up. Since there are no uplocks, you need to periodically boost the pressure in the system to make up for losses from imperfect valves and check valves. The up limit switches will turn the pump off again. If you can get your hands on the maintenance manual, the wiring diagrams should answer your question definitively.
Proud OOTSK member
 
Fly2HMO
Posts: 7207
Joined: Sat Jan 24, 2004 12:14 pm

RE: Seneca PA34-200T Landing Gear Question

Thu Aug 14, 2008 6:05 pm



Quoting Lowrider (Reply 1):
the pressure switch will cycle the pump on to hold the gear up.

This is how it is in the Seminole. Assuming no leaks or system losses, it shouldn't need to turn on again. IIRC, the cutoff pressure was 1400psi. I'm pretty sure most Pipers (at least those made in Vero beach) have the same common system.
 
meister808
Posts: 924
Joined: Sat Jan 01, 2000 11:45 am

RE: Seneca PA34-200T Landing Gear Question

Thu Aug 14, 2008 6:57 pm



Quoting Lowrider (Reply 1):
The up limit switches will turn the pump off again.

Ok, that makes a bit more sense. In the later years (Seminole, Arrow III), the system is different so that the pressure switch kicked the pump off once the pressure in the system hit 1800 psi or so, then would kick it back on if pressure dropped below about 1500 psi, thus eliminating most of the need for the uplimit switches, although they are still present.

Quoting FLY2HMO (Reply 2):
This is how it is in the Seminole. Assuming no leaks or system losses, it shouldn't need to turn on again. IIRC, the cutoff pressure was 1400psi.

Yep, mostly right there... I'm intimately familiar with the Seminole system, I could probably draw the thing with my eyes closed, pressures included... (1800 up, 1500 kicks the pump back on, high pressure control at 2400, thermal relief at 3000, low pressure control at 600, 450 down, the horn turns on at 14", between 10 and 25 degrees of flaps, or if the handle is selected up with weight on the left main... etc...)

 Cool

Meister
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation

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