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Matt,
The high side should read between 800 an 1,100 psi. The low side should be between 400 and 700 psi. Overshoots of up to 200 psi are normal and just fine. The pump itself has a 1,500 psi relief valve.
On Jul 5, 2006, at 10:50 PM, Matt Hapgood wrote:
Lorn, Pat, Chris, Jack and Vern;
I went out and did some gear retract/extension tests and recorded the results: here they are (it's confusing, and doesn't jive with what one would expect, so follow closely):
1. The last time I went out the plane, I took a lap around the pattern. The gear wouldn't retract, so I returned to ground, checked the pressure reading (about 1300 PSI), and went home to research the problem.
I think that your spool valve is in backwards and is not letting the down side pressure bleed to 0. When you put the gear in the up position, the down side pressure should immediately go to 0.
2. Returned to the plane today - pressure was down 900 - NOTHING had changed except the temperature was significantly cooler and it was cloudy vs. blazing sun.
Here's the sequence of what I did next:
3. Turned on the Master. NO pump blip.
4. Put the plane on jackstands
5. Bypassed the "squat" switch
6. Raised the gear lever - and, as expected, the gear retracted perfectly.
7. Pressure on the gauge read 0 as soon as I raised the handle, and stayed there after the gear was retracted and the pump shut off. This indicates it is reading the low side.
I agree.
8. Lowered the gear handle.
9. The gauge read about 0 the entire lowering process, then, at the last second before the pump shut off, it went to about 800 PSI.
It doesn't take any real pressure to lower the gear. The down side pressure is used to keep the gear down. Again the down side pressure should be between 400 and 700 psi.
10. Turned off the master
11. Opened the dump valve, and the pressure dropped - but only to about 400 PSI.
It should have gone to zero.
12. Closed the dump valve (pressure stayed the same).
13. Turned on the master - the pump "blipped" and the pressure went to about 900 PSI.
This 900 should have been 700. But all pressures can overshoot by up to 200 psi.
14. Raised the gear (same results as 6 - 7).
15. Pulled the pump CB.
16. Opened the dump valve. Result - IMMEDIATE freefall, gauge read 0 the entire way.
17. Lowered the gear handle.
18. Pushed in the CB.
19. Pressure ran up to about 700 PSI.
20. Master off.
21. Opened the dump valve - pressure dropped to about 300 - 400 PSI.
Something is stopping the drop (the spool valve?). The pressure should always go to 0.
22. Turned on the master - bump blipped up to about 900 PSI.
I repeated this process several times and got virtually identical results.
I then decided to adjust the low pressure switch (it is the adjustable type). I backed the adjustment screw out 1 turn and then repeated steps 14 - 21. This time, when I turned the master on, the pump didn't blip. This suggests my low pressure set point was now below 400 PSI. I played around with this process several
times before getting the pressure to 550 PSI, then turning the screw just until the pump blipped. Before I think the pump was set about 650 - 700 PSI, and now I think it is about 550 PSI.
There is a 300 psi spread in the high and low pressure switches. The 550 that you are set at makes the low side go down to about 250. 250 is pretty low. Remember that is what is holding the gear down. It is probably OK. It doesn't take much to keep the gear down.
That may help matters, but it's not the real problem.
An interesting conclusion is that the low pressure limit may be set to 550 PSI, but the pump can't seem to shut itself off quickly enough, so the pressure can still get as high as 800 or even 900 PSI.
Based on what some of you had told me, I've got something funky going on with the dump valve. It drops to zero on free fall tests, but does NOT drop to zero when the gear is already extended. Any thoughts? Can any of you confirm what your planes do in this situation?
My dump valve started leaking in about 1999. I ordered a new one from Lancair and it has worked fine ever since.
At this point I am very confused, still, about why my pressure is increasing on those hot days to over 1200 PSI, and why it can also decrease later (as I witnessed today vs. two days ago). I'm also very confused about this whole dump valve thing.
The dump valve doesn't just let the pressure go from the high side to the low side. It must also let the pressure get out of the pump in order for the pressure to get to 0. Something is wrong in your pump. Either your spool valve is in backwards or your pump has something sticking and needs to be rebuilt.
I had my pump sent to Oildyne in 2002 along with my new (from Lancair) pressure switches and had everything rebuilt and pressure tested. My quoted price at the time was $75.00. They found my spool valve reversed even though my plane had been flying fine that way for more than 4 years. I bought the pump new from Lancair in 1998.
OilDyne's contact information is:
Edward Van Hecke
voice: 763-531-3578
5520 North Hwy 169
Minneapolis Mn 55248
Please help!
Sincerely,
Matt Hapgood
919-933-3295
ps. I haven't removed the spool valve, but it doesn't look that difficult to do - it is accessible without removing the pump.
--
Lorn H. 'Feathers' Olsen, MAA, DynaComm, Corp.
248-345-0500, mailto:lorn@dynacomm.ws
LNC2, O-320-D1F, 1,200 hrs, N31161, Y47, SE Michigan
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