Hand pump overflow

[aw113sgte]

Had this problem for a while now, with two different pumps.
When lowering the cab (allowing gravity to do it slowly - no pumping on the way down) I get hydraulic fluid pushing out the vent plug. It will do this on successive raise/lower cycles until it pushes out enough I can't even raise the cab (reservoir empty). I have the air/oil pump completely removed (it overflowed when that pump was still on there). The kneeling cylinders are also removed and all lines capped at the manifold. I have no leaks under pressure in both directions for cab tilt (pump handle gets hard and I keep pressure on it and it does not move and no fluid at any fittings).
Spare tire system seems to work just fine, haven't had an overflow when using it. The cab cylinder does not leak down under pressure (can have cab half tilted and it will sit there indefinitely).
Seems like the cab tilt cylinder is not pulling any fluid from reservoir for the low pressure side of the piston (so if must be pulling air in - or have enough air in it so it doesn't pull much fluid and the air is increasing in volume under vacuum?
I'm considering removing the ball and check from "raise" side of the cylinder to see if maybe it's restricting flow but besides that...I don't have any great ideas.

 

[Ronmar]

the hand pump is not supposed to be vented on the OEM system, by design it must be completely sealed with a plug and the vent is at the Air-op pump... you may need to do some plumbing alterations as I do not believe the return side is able to draw fluid from the hand pump reservoir on the OEM style hand pump...

 

[Ronmar]

In the end, if you send 10oz to the cylinder to lift the cab, you should get that same 10oz back. The little bit of fluid you send to the rod end to get back over the balance point when lowering should be forced back on the next raise.
The checkvalves should be of no consequence if the lines to the AOP are capped, as the fluid has no choice but to return to the hand pump.

There is no guarantee the cylinder rod end will draw fluid thru the pump restrictions, as the seals on the rod end and pump piston/shaft were designed to withstand pressure, not vac.

The pump itself, in conjunction with the check valves was designed to self fill and draw additional fluid from the AOP res as needed. They were really designed to work as a system, so something else could be causing issues, if all the parts are not in play

Yet another reason i swapped AOP, manifold and sealed hand pump with a standalone hand pump. Far simpler, less parts to go wrong...

 

[aw113sgte]

From the diagram, it sure looks like it should pull from the reservoir. Even if the return pickup is high, it should pull fluid before overflow can happen.
Check valves don't look they would be in play at all.
I wonder if the cab latch may have a leak under vacuum as it could pull air from the vent....hmm

 

[Ronmar]

the cab latch is never really under vacuum...

There should be no possibility of overflow on the hand pump as it has no vent to overflow as built to this diagram. it has a plug9shown on diagram) The system vent is in the air-op pump reservoir... So when fluid returns, it should flow to the hand pump until that line builds enough pressure(5PSI) to open the check and start returning fluid to the AOP. When using the hand pump, if it expends enough fluid to create 1PSI worth of vacuum, it should draw fluid from the AOP reservoir thru that second check valve.

did you cap the lines to the AOP, and how is the hand pump vented?

 

[aw113sgte]

the cab latch is never really under vacuum...

There should be no possibility of overflow on the hand pump as it has no vent to overflow as built to this diagram. it has a plug9shown on diagram) The system vent is in the air-op pump reservoir... So when fluid returns, it should flow to the hand pump until that line builds enough pressure(5PSI) to open the check and start returning fluid to the AOP. When using the hand pump, if it expends enough fluid to create 1PSI worth of vacuum, it should draw fluid from the AOP reservoir thru that second check valve.

did you cap the lines to the AOP, and how is the hand pump vented?

Yes, hand pump is vented to atmosphere with the specified venting cap from the manufacturer.
Yes AOP lines are capped.

 

[Ronmar]

and with the AOP lines capped, and it the only pump in he system, it would have to be vented...

back to the basic premise, this system takes X amount of fluid(the number is in my notes at home) to lift the cab.

what is the volume of that pump? It takes 24oz to lift the cab, with only a small fraction returning

In practice mine has never sucked fluid into the rod end of the cylinder either before or after I swapped to the manual hand pump system. the reason I know this is that there is a restricted orifice screwed into the rod end cylinder port to help control the cab lurch as it passes over the balance point when raising, like the restrictor in the control valve limits lowering speed when lowering. you should be able to feel an increase in pumping resistance as you approach the balance point when raising the cab. that is the small volume of fluid used when you last lowered the cab, finally being pushed thru that restrictor near the top of the stroke and causing a small increase in pumping load.

So if you pump say 24oz/.19ga; to lift the cab(the cab latch absorbs a few oz also), you would expect to get back maybe 3-4oz from the rod end at the top of its stroke. when you lower you would pump those 3-4oz back to the rod end and receive 24 ounces back from the base end as you lower. so the reservoir only exchanges 20oz, but must be able to hold 24.

if the reservoir is large enough this process should find equilibrium where you can cycle the cab up and down without venting fluid…

 

[aw113sgte]

and with the AOP lines capped, and it the only pump in he system, it would have to be vented...

back to the basic premise, this system takes X amount of fluid(the number is in my notes at home) to lift the cab.

what is the volume of that pump? It takes 24oz to lift the cab, with only a small fraction returning

In practice mine has never sucked fluid into the rod end of the cylinder either before or after I swapped to the manual hand pump system. the reason I know this is that there is a restricted orifice screwed into the rod end cylinder port to help control the cab lurch as it passes over the balance point when raising, like the restrictor in the control valve limits lowering speed when lowering. you should be able to feel an increase in pumping resistance as you approach the balance point when raising the cab. that is the small volume of fluid used when you last lowered the cab, finally being pushed thru that restrictor near the top of the stroke and causing a small increase in pumping load.

So if you pump say 24oz/.19ga; to lift the cab(the cab latch absorbs a few oz also), you would expect to get back maybe 3-4oz from the rod end at the top of its stroke. when you lower you would pump those 3-4oz back to the rod end and receive 24 ounces back from the base end as you lower. so the reservoir only exchanges 20oz, but must be able to hold 24.

if the reservoir is large enough this process should find equilibrium where you can cycle the cab up and down without venting fluid…

Reservoir volume is .6 liters (20.3 fl oz)
I am able to tilt the cab and lower the spare, then raise the spare and start the cab coming down. If I manually pump while the cab is coming down, it does not overflow. It seems very odd to me, that I can lower the cab, the reservoir overflows, then I can raise the cab, then lowering it overflows again. It shouldn't overflow unless something else is displacing the volume in the system as it's a closed system (except for the vent). Then after enough cab raises it pushes out enough fluid that it can't raise to balance (runs out of fluid).

 

[FarmingSmallKubota]

Yes, hand pump is vented to atmosphere with the specified venting cap from the manufacturer.
Yes AOP lines are capped.View attachment 921352View attachment 921353

That is the wrong plug on the hand pump. My hand pump only has an allen head plug unvented and is only used to fill the hand pump

 

[aw113sgte]

That is the wrong plug on the hand pump. My hand pump only has an allen head plug unvented and is only used to fill the hand pump

Not for when the AOP is removed.

 

[Ronmar]

Well that reservoir isn’t large enough to take the 24+ oz from the cylinder base(and that returning from the latch cylinder), and by pumping when lowering, you are using the rod end of the cylinder as aux storage…

 

[Ronmar]

You can add more storage… remove your vented plug and install a hose barb. connect a hose and run that to the bottom of a second small tank/container. You could form one from pipe and fittings, you only need a few oz, and re-install that vent plug on top of the added tank/reservoir. This will up the 20OZ capacity of your hand pump to whatever you choose it to be…

 

[aw113sgte]

I'm really not following. It has more than enough volume to raise the cab, so when lowering, that same volume should return to the reservoir. Instead I'm getting more back than I pumped out.
I really think there is another issue here, as when I had the AOP, the hand pump would become empty and the AOP would overflow. This was with the non-vented fill plug.

 

[Ronmar]

well you said after it burps a time o two, it wont have enough fluid to raise the cab again right? Since the reservoir is at least 5oz smaller than what the cylinder and latch require, I suspect it is ingesting some air very near the top where you don't need much force anyway as you empty the reservoir, about the time it starts getting fluid back from the rod end. These air biscuits go to the base end of the cylinder, but float to the top near the piston, so when lowering, it pushes any fluid out first, and again, the reservoir volume is 20% too small to hold that total cylinder volume. you need a larger reservoir, close to 30oz.

plug a hose into the vent hole and run it up to a funnel or some other container that can hold another 5-10oz and cycle the cab a few times, and I think you will see that it will work just fine with just a little more storage volume... Remember, the original config could draw from the AOP reservoir as needed...

 

[Ronmar]

Or you could partially restore the added volume of the original 2 reservoir system. Reconnect the line on the manifold valve circled in green to the bottom of a vented reservoir, and replace the vent on the pump with a sealed plug…

also, you need to make sure you get all the air pockets out of the system before you use the tire hoist. Air in that cylinder can cause it to hydraulically lock…

 

[aw113sgte]

After raising the cab all the way, I've been able to use the tire hoist just fine, indicating enough fluid. Maybe I do have air bubbles messing this whole thing up.
I removed the balls/springs from the tire hydraulic a while ago as I often had issues with them locking.
They do make a reservoir that's double the size if I need to go that route.

 

[Ronmar]

Yea but that is just the opposite scenario. Lowering the tire is like lowering the cab, it only takes a little fluid to get the tire or cab over the balance point… When raising the cab, the cab passes the balance point and finishes extending the rod end fully. This pushes that fluid back to the reservoir that was placed there the last time the cab was lowered, giving you a few oz to work with in the reservoir, enough fluid to push either the cab or the tire over the balance point . That is enough fluid to push the tire cylinder the short distance past its balance point, and since its rod end is completely full of fluid from the previous lift, it is pushing fluid back to the reservoir the entire time the tire cylinder is extending/tire is being lowered, which is exactly how much fluid it takes to raise the tire back into its cradle….

the simple fact is it takes ~24oz, plus whatever the cab latch requires, to lift the cab… Your reservoir is only 20oz… in the immortal words of… well someone, “Thars your problem right thar”… It will continue to be problematic until you increase the reservoir size so there is no possibility of sending air to the cab cylinder base While raising the cab…

I have suggested a few simple ways to expand your reservoir size and confirm this is the case.

good luck with whatever you decide…

 

[aw113sgte]

I'm wary a large reservoir will cover up a separate problem (hand pump would empty when I had the AOP and AOP reservoir would overflow) but it wouldn't hurt to have some extra volume. $42 for a larger reservoir-double the capacity. I'll give it a shot and I'll also try to bleed out the air in the system.

 

[Ronmar]

Well in the original system the hand pump will only pass fluid when you pump it. If fluid wasn’t returning to the hand pump, that sounds like a clogged return path that forced all returning fluid to the AOP.

bleeding is fairly simple, lower the cab fully, disconnect the base end hose, place it in a container and pump a little. That pump is .25 cu inch per pump, 1/4” line has a .049” cross section, so each pump fills about 5” of line, so 15pumps for 6’ of line? Then reconnect the line to the cylinder. Then disconnect the cab latch line and do the same thing, perhaps another 12 pumps for the length of line from where it branches off the main line up to the latch.

Lower the spare and disconnect the cylinder rod from the crane structure. Stand the cylinder straight up on its base end pivot and retract the rod using the pump with the valve in the raise position. Let it set for a minute so any air bubbles in the fluid in the rod end will go to the top of the rod end. Now shift the valve to the lower position and use the pump to fully extend the rod. With the cylinder pointed straight up, any air on the rod end will be forced out of the cylinder first and back to the reservoir. Go ahead and extend and retract a second time to be sure, then lay the cylinder down, re-attach it to the crane and stow the spare…

the cylinder end with the cylinder port on top always self purges, which is why you need to pull the hose off of the cab cylinder base. Because the air is the last thing pushed out of the cab cylinder base, that line could be completely full of air. If you pump for a while before anything seems to happen when lifting the cab, it probably is. you must first compress all the air in the line enough to develop enough pressure to start performing the work…

By rotating the tire cylinder straight up you temporarily make that the self purging end, which is way easier, as that end will push any air back first, so you simply need to cycle it to send any air back to the reservoir where it can separate and escape thru the vent…

 

[aw113sgte]

Thanks for all the info! Reservoir ordered, I'll probably order new hoses too as I think they are original. Bleeding process is helpful, and with me changing 3 things at once, I'll have no idea which thing fixed it (fingers crossed it is fixed).