Had an issue on my 2 post on Sunday. Had a truck up in the air, was bringing it down near the ground, and I stopped the lowering and it kept coming down to the next lock. I went to put it up again and nothing. It wouldn't go up at all. We ended up taking the truck off the hoist with a jack(one corner at a time). Lucky it was only a few feet from the ground.
I was able to get the hoist down by jacking each arm to release the lock and let it lower to the ground. It wouldn't go up at all, I went thru the bleeding procedure in the manual and am now able to lift the hoist up, but it then just falls to the ground again. It is not holding pressure.
I am assuming the only thing that holds pressure on the hydraulics is in the power unit, the button you press to lower, would release the fluid back into the reservoir.
I stopped the lowering and it kept coming down to the next lock. I went to put it up again and nothing. It wouldn't go up at all.
The lowering valve would just be a manual operated (? or by solenoid, I guess it doesn't matter) pressure relief, return to tank, maybe that's got dirt holding hyd. circuit open. It would see a lot of flow. That would explain both symptoms.
fluid levels ok? can you check the pump output pressure and compare to a spec? stick a fitting and a gauge on it maybe.
I don't know anything about them, but maybe check that a pressure relief valve isn't stuck open, or maybe a check valve on pump output side that is bleeding pressure back.
With the moving and setup, I bet there was lots of banging and shaking that could have dislodged dirt/rust and contaminated the fluid.
Did you change fluid with the move? Maybe flush and clean fluid once you get the major problem figured out.
Is there a filter on it?
do much 'net searching for your unit or general hyd. schematics for lifts?
Fluid level is fine. I checked all the fittings for leaks as well. I did not change the fluid when I got it installed, but had most of the fluid lost out of the system during setup with the bleeding procedure that I had to use.
I am going to take the power unit off and remove the relief valve and the manual release valve to inspect them.
Lowering valve is located in the pump. System would either have pressure on it from the pump, holding the cylinders up, or have no pressure in it with the hoist fully lowered, or in a position on a lock.
Maybe what you wrote can be taken a couple of ways.
define components: pump: provides pressure/fluid volume electric w on/off switch (fluid flows to cylinders) check valve: holds pressure after pump (cylinders now have set volume of fluid, can't move) lowering valve: manual bleed to release pressure (fluid flows to tank, lift lowers) relief valve: bleeds pump pressure to tank, if lifting too heavy. Safety item. (pump runs, pressure is not enough to lift heavy load, relief valve spring is overcome, pressure bleeds to tank, no cylinder movement)
the first two valves stuck open would cause your condition. (will raise w pump on, then drop w pump off, didn't lift w truck on hoist, but will with no weight) The pressure relief valve jammed open would not allow the lift to raise, pump would just put fluid back to tank. maybe the check valve and lowering valve are the same unit, manual control lever? dunno.
Since the problem happened with the truck close to the ground, after lowering (I assume) you worked on it a bit, then it wouldn't raise to get off the mechanical locks? That fits with lowering valve stuck open. The pumps runs, and just spits back to tank, can't make cylinder pressure. With no load after you got the truck off the lift, it works a bit because pump has enough no-load capacity to overcome the 1/2 open lowering valve.
The bypass is for timing the right side... the flow control just slows the fluid down when returning to the tank.If you take it out and put a pipe in there it will not go down.. must be a saftey valve in the pump so it cant drop... to much flow and it stops
I am convinced it is a lowering valve stuck open as well Jan. I spoke with both the manufacturer of the pump unit & a local hoist repair guy that was recommended by Bruce @ Strickly. They are easy to take apart and clean. Will also change the fluid and clean the screen when I have it apart...
Will report back my findings!
Switch...push up raises the hoist, pull down lowers the hoist.
So I was able to spend some time taking apart and cleaning the release valve.
First step to remove the reservoir.
There is a ball inside this valve that I could move with a screwdriver. It wasn't seated properly when I started...I was able to get some dirt out of it. I expect there is still more between this valve and they connection point/pump that I can't see.
It will now hold pressure while it's up, but as soon as I release it, it comes all the way down. It should stop/start with that valve.
I am going to take the unit off and drop it off to a guy in Burnside that works on these all the time. He is going to take it all apart and clean it for me. I will flush out the hydraulic lines on the hoist as best I can in the meantime. Hopefully all new clean fluid with this will fix my issue for good!
Post by Diffsmasher on Feb 20, 2014 11:30:52 GMT -4
If the pilot operate check valve is not integrated with the unit I would check it as well. When I worked at Dalhousie there were certain pilot operated PRV's (pressure reducing valves not pressure reliefs) that would stick wide open every time we did a steam shutdown.
Got my power unit back today. Ended up having electrical tape inside the lines/pump. No idea how it got in there, but explains the bits that I pulled out of the release valve, I guess there was one piece inside that was 2" long.