Hydraulic Pump running at switch on

tropical · #1 03-11-07, 07:51 PM

i've noticed on my skymaster (74 G model) after it's sat for a week i turn on the master switch and the hydraulic pump runs anywhere from 10 seconds to up to 45 seconds (est). is this normal for the electric powerpack models? my previous experience was with a 66 A model i owned several years ago.

Ernie Martin · #2 03-11-07, 10:54 PM

I have a '73 G model in Miami, which has a powerpack. It's normal, if the aircraft's been sitting for a while, for the doors to be slightly open, so the microswitches activate the powerpack to firmly close the doors. But this should take only a few seconds. In mine, maybe 5 seconds. Ten seconds wouldn't concern me, but anything above that -- and certainly 45 seconds -- would cause me to have my mechanic look at it.

Ernie

tropical · #3 03-11-07, 10:59 PM

i was just reading the maintenance manual, and there is a mention of a hydraulic accumulator and the mention of charging it to 500psi. it would stand to reason if the accumulator was low this may cause this problem.

i'll look into it more. btw, i am also the mechanic.

Pete Somers · #4 03-14-07, 04:10 PM

The accumulator is to keep the doors closed while the a/c is on the ground with no power on. If the doors stay closed ok the accumulator is ok.
If you have not used the a/c for a week the pressure switch may be a little sticky. Also a low battery will not allow the pressure to build up to shut off the motor.
Before you start the engines pull the gear c/b and push in after you have started and see if the pump run ok then.

Pete

tropical · #5 03-15-07, 09:07 PM

i've been powering up the aircraft everyday this week, and the pump doesn't come on when i energize the master.

after the plane sits for a few days, i get a little sag on the gear doors and a quick run of the hydraulic powerpack to close them when powered up.

from what i've read in the service manual, it appears i need to charge the accumulator. however, the service manual doesn't give any information on location of the accumulator, it only says charge to 500psi.

Pete Somers · #6 03-16-07, 03:10 AM

If you look at figure 5-38 page 5-67 you will see a system schematic. The accumulator is on right, it is charged up by the pump and a check valve is in line to keep the accumulator pressurised.

Pete

gfcudahy · #7 03-18-07, 09:50 PM

A picture of the accumulator is on page 5-30, Figure 5-13A in the service manual. The service manual states it is in the center tunnel approximately at the rear part of the front seat tracks - inside the pressure hull. But, first check to see if you have an accumulator - the early P's did not come with one. My 1973, SN 0039 does not have an accumulator. The spec says the hydraulic pack cycle time, with the gear up or down (door closing pressure) should be greater than 10 minutes. Mine, with no accumulator, excedes 20 minutes - I quit timing at 20 mins. I check the time periodically to ensure I do not have one of the door cylinders leaking around its piston. That has happened to me in the past. The check can be done on the ground on the battery - it is easier to hear it then.
George

Ernie Martin · #8 03-18-07, 10:58 PM

Do you mean seconds? 10-20 minutes sounds like way too much.

Ernie

gfcudahy · #9 03-19-07, 12:00 AM

Ernie,
The "trouble shooting" section, page 5-6D, for the door sagging problem states the test of the thermal relief valve and the lock out valve should hold test pressure for 10 minutes and door test pressure should not bleed down. I use 10 minutes and test to 20 minutes. For your info I also just recently had a red light(same as gear up/down lights) installed next to the gear down light in order to monitor the pump on condition - the light is on when the pump is on. The pressure switch is supposed to turn off(works only in the door closed condition, otherwise the pump runs) at approx. 1500 PSI and on at approx. 1100 PSI - page5-53.
George

sunnysky · #10 03-28-07, 01:50 PM

But I agree with Ernie. No way should the pump run for the time you are saying.
SunnySky.

sgmret · #11 03-28-07, 02:22 PM

Although I don't own a Cessna 337 at present I have owned two in the past. My first one was a 1973 G-model and the second a 1977 G-model. Shortly after I bought the first one in 1975 I had a mechanic give me what I considered some good advice at the time and I used it during the periods I owned both airplanes. That advice was to check the hydraulic gear pressure before each flight. He advised that before turning on the master switch or any other accessories, extend the gear handle and pump the doors open. Thereupon one can check if there are any leaks inside the doors. He cauthioned not to move the gear handle and that one can determine if the doors close tightly and securely as soon as you turn the master switch on as that activates the electric motor and closes the doors. Occasionally the gear doors were slightly opened if the aircraft sat for too long a period - perhaps two weeks or more.

Perhaps others have received the same advice and found it helpful as well.

sunnysky · #12 03-28-07, 02:36 PM

Yes. I always do this on pre flight. When turning on the master, the pump maybe runs for 5 to 10 seconds, to close the doors. Or if I haven't opened the doors with the hand pump, on turning on the master, the pump may run for 1 or 2 seconds just to "nip close the doors". All normal stuff, but no way should the pump run for minutes.
SunnySky.