Hi Bob / Wolf,

 

Thanks for your advice.

 

My old 12 year old accumulator (recharged to 600 psi last October) was my first guess – I put a new one (with 625 psi charge) in 2 days ago and was hoping the problem would go away – everything remained the same.

 

Anything is possible when it comes to electrical (I believe this especially after finding out that a stuck mike message in my GPS came from a worn trough heat shrink tubing at the plug for my pilots head set). I do not have any wiring back there where the flap motion is going on. I did not put a flap switch in and my gear switch wiring goes to the rear (away from the motion) and is protected by tubing. Also the pump seems to come on always at the same flap position during movement. I could be wrong but I don’t think I am grounding a wire by accident during the motion.

 

The gear cycling works fine – the pump comes on very shortly after moving the gear down lever and stays on during the motion. When the motion is complete the pump continues to run for approx 2 – 3 sec. It happened already 2 or 3 times that after the pump went off it came on again for a very short time (0.1 sec) approx 1 or 2 sec after it stopped the first time (it almost felt like a wave going through the system after the accumulator was filled up and triggered the pressure switch for a moment).

 

When I don’t have any hydraulic action going on my hydraulic pump remains silent. It does not come on by accident.

 

When I bleed my hydraulic pressure (pull circuit breaker and move flaps) and push the circuit breaker back it the pump fills the accumulator back up and stops then. Sometimes it happens that the pump comes on then again after 1 or 2 sec for a duration of 0.1 sec (similar to my wave theory from above).

 

When I pull the circuit breaker, do one flap cycle, put the circuit breaker back in, the pump comes on for approx. 1 sec (duration is similar to what I see during the regular flap cycle)

 

The more I think about it the more I would like to try your pressure switch to see if it makes any difference in behavior.

 

Thanks

 

Ralf

 

 

Ralf wrote:

 

When I move my flaps down at about 70% of the travel my pump comes on for approx 0.5 to 1 sec. The flaps then retract without the pump coming on. When I move them down again at 70 % travel the pump comes on again. (the pump is continuously on when it starts up – it does not come on and off in very short intervals)

 

When I pull the circuit breaker I get almost 3 complete flap cycles out of the accumulator.

 

I tried to bleed out the air from the system at the fittings of the flap cylinder, the accumulator and the bulk head where it goes under the rear seat. I do not get any air – just oil.

 

When I filled my hydraulic system the first time I did not have this problem – I got approx 1.5 flap cycles before the pump kicked in.

 

I changed two things in the mean time:

1. I increased the flap cylinder stroke by approx 5 mm (1/4 “) by adjusting the hard stop.

2. I removed and put back in all hydraulic lines that run from the front to the rear of the cabin on the floor (I found a significant cabin pressure leak in the tunnel for the hydraulic lines under the front seats that needed to the fixed)

 

The function of flaps and gear works fine. Is the described situation acceptable or do I have to worry about air in my system that needs to come out (and how to get it out if so)

 

 

 

Ralf,

In my opinion, the pump coming on for “0.5-1 second” is not normal for an IV-P hydraulic system with a functioning accumulator, which seems to be OK from your later description. I can’t imagine how air in the system could cause this cycling, but have seen strange things with hydraulic systems, so perhaps it’s possible?

 

It sounds to me like the pump relay is being triggered by something other than the pressure switch. Is there any chance you have a bare or pinched wire in the pressure switch wiring that’s being momentarily grounded/shorted during flap movement? I don’t mean to insult your intelligence or craftsmanship, especially after looking at the enclosed picture, but one of the purposes of the accumulator is to keep the pump from “cycling” like this, and according to your description above, it does so for other operations. Do you get any “blips” when cycling the gear?

 

My system engages the hydraulic pump with each flap extension, meaning I probably have less accumulator “capacity” than you do before the pressure drops below the switch trigger level. These switches have a range of open/close trigger values that affect this “capacity” as well, but the very short pump runs are, again, not normal.

 

If you don’t find a wiring problem, consider changing the pressure switch. That’s the easiest thing to do in the troubleshooting line. I have a spare in my tool kit that I could loan for this purpose if you’d return/replace it after your test. Contact me off-line if interested.

\

Bob