Overfilled floor jack & bleeding

[cparke]

I know these are classic questions, but the instructions and advice I found still keep me puzzled.

I changed the oil in my floor jack, because the old oil had become black and watery. I did not understand from bleeding instructions that the cylinder must not be full. That means, of course, there is always air in the cylinder, unlike how other hydraulic systems like a car's brake fluid typically have no air (I guess that may not be entirely right---brake fluid tank does have a level indicator and obviously there is air above that).

So I definitely overfilled my jack and seem to have blown the seal on the release valve, because oil is leaking out when I open the release valve and I keep getting air pressure building up inside the jack when using. Otherwise, it seems to be working surprisingly and never experienced hydraulic lock. It also held the car up at full height for one hour fine.


This leads to several questions:

1) O-rings are the "seal" we're primarily talking about, especially when it comes to the relief valve? I don't see any other type of seal on the release valve screw when I take it out.

2) If hold the position the jack up vertically, does the fill hole usually serve as a max level fluid indicator like it does on many bottle jacks that stand in that same orientation?

3) For bleeding, can I instead simply remove the release valve while the jack is vertically upside down (i.e. release valve is at the top so fluid doesn't drain out) as an alternate method of releasing excess air inside the jack? This seems much easier than repeatedly removing the rubber cap.

4) Through the bleeding process by pumping while release valve is open and jack is on the ground normally (horizontally) with the fill plug removed, will the excess fluid also naturally come out during pumping?

5) When lowering the jack, I noticed a few times that the pumping lever would pop up when the jack reached the bottom, but would fall on its own once closing the release valve. Seemed really strange to me. Is that a sign of excess fluid or air still in the system or normal behavior? I never recalled happening before on any jack.

6) Is it true that bleeding should include squeezing the rubber plug for a moment to burp air when the lack is fully extended after overpumping it up? Seems like a way to add air into the system to me, exactly what I don't want.

7) How do I know when all the air is really out of the system? I keep seeing more air build up as I repeated the process, but I surmise the leaking seal on the release valve when it is open could also be allowing air to enter the system so it can never be finished bleeding?

8) The pump plunger seems to not be leaking and the jack is working despite the overfill, so I assume those seals and the ucup were not also damaged and I shouldn't bother checking them?


I might have forgotten some other questions, but I think that covers the most important stuff.

Thanks in advance for all your thoughts.

 

[5ubtle]

I'm no expert, but these are my opinions:
1) yes
2) I don't know. Don't worry about the level. If there is too much oil, it will come out (see #4). If the saddle will not go up all the way, you may need more oil.
3) The rubber fill plug is only there to 'keep dirt out' and to 'keep the oil in while the jack isn't on level ground'. No need to remove-replace-remove-replace plug while bleeding. Just leave it out while bleeding, if that makes you happy.
4) After bleeding, take out the fill plug and lower the jack. Any excess fluid will come out of the fill port.
5) I don't know. If this is your only concern, then "don't worry about it".
6) Burp the plug when the jack is down because you are going to store the jack down. There is always some air in the reservoir. When you jack it up, a vacuum forms in the reservoir. Later when the saddle comes down, the reservoir pressure returns to normal.
7) Endless air entrainment is usually caused by a bad pump piston seal
8) See #7. The pump piston seal might not leak oil, but could allow air to pass the other direction.

 

[mikedodge]

You shouldn't have to put the jack up on end to bleed it or fill it.
It doesn't matter if there is air in the reservoir, the oil is being pulled in from the area that's submerged.
If it's overfilled the oil doesn't have anywhere to go when you lower the jack. It'll either find its way out past one of the seals or if there's no load on the jack it might not come down all the way. If it's over filled you can use a syringe to remove some of it or a messier way make sure the jack is clean around the fill hole and start tilting it with the cap off and let a bit pour out.

 

[cparke]

Very helpful replies from both of you. Thank you so much! Very revealing about how this thing really works and how these issues cause problems.

 

[cparke]

I changed the o-rings on the release valve and the piston, and that seems to have resolved the oil leak from the release valve when lowering and the apparent constant air buildup in the reservoir when trying to bleed.

So I am left now with with one last puzzle; air pressure vs. reservoir fluid level. I am finding that if I relieve the air pressure in the reservoir when the floor jack is down with the plunger also down, then when pumping to lift, it stops lifting very early. Surprisingly, this appears to be due to vacuum in the reservoir, for if I simply relieve that vacuum at this point in raising, then pumping resumes lifting the jack all the way up. However, when lowering, I find that the plunger pops up on its own when the jack reaches fully lowered position. It seems that air pressure in the reservoir when fully lowered (because I added air while lifting) is what is pushing the plunger up.

Ok, so is it normal for the plunger to raise itself up when the jack is fully lowered? Or is this an indication of too much or too little fluid in the reservoir? I find it especially strange that simple air vacuum in the reservoir is strong enough to stop the cylinder from rising during pumping, as I am observing.

Additional Info: This hydraulic floor jack has just a rubber plug for the fill valve. It does not have a breather cap or port to relieve pressure when lifting and dropping.

 

[5ubtle]

Thanks for telling us how you got along. Many people never tell us how it works out.

I am finding that if I relieve the air pressure in the reservoir when the floor jack is down with the plunger also down, then when pumping to lift, it stops lifting very early. Surprisingly, this appears to be due to vacuum in the reservoir, for if I simply relieve that vacuum at this point in raising, then pumping resumes lifting the jack all the way up.

The pump fills by creating a vacuum so that fluid comes in from the reservoir. If the reservoir vacuum gets too big, fluid can't flow to the pump?

is it normal for the plunger to raise itself up when the jack is fully lowered?

I don't know if it is normal, but I "live with" mine doing this. "More import things to worry about" and all.

Additional Info: This hydraulic floor jack has just a rubber plug for the fill valve. It does not have a breather cap or port to relieve pressure when lifting and dropping.

A breather does seem like a good idea, but I've never seen one of a jack. It's always been just a rubber plug.

 

[cparke]

I guess it's a delicate balance as I understand it.

Too much fluid means less air in the reservoir and a stronger vacuum when lifted. Plunger up when jack is lowered is probably a good thing actually to allow extra air to sit above the reservoir, causing less vacuum to develop while lifting.

So if that's what's going on, how do I determine the minimum fluid level needed? I'm assuming the reservoir can be almost empty when the jack is fully raised, I could just drain the reservoir while in that state?

 

[5ubtle]

The only downside (that I can think of) to having the plunger up is corrosion over months (years of storage).

I'm assuming the reservoir can be almost empty when the jack is fully raised, I could just drain the reservoir while in that state?

Sounds good to me.

 

[ajchien]

Any chance you can share a pic of your jack’s hydraulic cylinder/block or its brand/model?

a general rule of thumb is that when you’re peering into the reservoir through the small fill hole, you’ll see the inner cylinder. When the jack is completely lowered, the oil should be just above/covering the inner cylinder.

usually the plunger/handle won’t go up when the jack is fully down. I’d suspect that one of the valves isn’t working quite properly under that condition.

the jack stopping its lift, and then restarting when you equalize pressure by relieving the reservoir vacuum suggests that the seals on the plunger responsible for pumping the oil from the reservoir to the lifting cylinder have weakened, likely also from long term overfilling the reservoir. Yes, jacks with vents in the fill hole instead of a plug will not build vacuum in the reservoir, in theory, it prolongs the life of the seals.

 

[cparke]

Jack hasn't been overfilled very long. I drained it recently and then filled with new fluid, which is why I'm concern now about proper fill level, because I've never done something like this before. I also just changed the o-rings as part of this tune-up. Jack and has been in periodic use for about 10 years and been working correctly. Jack seems to still work fine now too, just dealing now with this quirk about the vacuum vs. excess air in the reservoir and want to get that right too.

So I don't think there's a problem with the jack's valves, but I do suspect it is slightly overfilled. Jack fluid is above/covering the inner cylinder when looking down into the fill hole, but I'm not experienced enough to know where the fluid level should be, what that looks like.

Maybe this series of related questions is what I'm trying to answer here:

1. Are these issues---jack stops going up midway until vacuum is released, plunger rises by itself when jack fully lowered---possibly symptoms of being overfilled?
2. If so, should I just gradually remove fluid to see if the issues hopefully go away?
3. When re-plugging the fill hole after adjusting fluid while jack is lowered, should the plunger be up or down?
4. How much fluid should be left in the reservoir while the jack is fully raised?

 

[mikedodge]

It's hard to determine how much fluid should be left when it's fully raised. Enough that it won't run dry as it seeps out anywhere with normal use but not so much that it won't come back down.

It doesn't make a difference if the plunger is up or down but up is typically the default location most spring back to.

Leave the fill cap off and see what happens. That will eliminate the thought of vacuum and air pressure causing issues.

If you have to drain some oil use a syringe or messier way make sure its clean around the hole and tilt it.

 

[cparke]

I know it works without issue with fill cap off and these issues are vacuum/air pressure related issues.

Fluid level an ambient air volume is all I can really modify. It's surely air tight and seals are working (leak-down passes).

 

[Hiball]

I know it works without issue with fill cap off and these issues are vacuum/air pressure related issues.

Fluid level an ambient air volume is all I can really modify. It's surely air tight and seals are working (leak-down passes).

As already stated, if the jack operates normally with the plug removed, it’s a weak pump seal. It’s not that complicated of a system.

 

[cparke]

Ok, so we're saying the seal should be able build up a bigger vacuum without a fluid seeping back into the reservoir?

So to fix this, I would have to fully disassemble the pump itself and remove the cylinder? I guess we're talking about the seal the bottle of the cylinder or something called the 'ucup'?

 

[Hiball]

Ok, so we're saying the seal should be able build up a bigger vacuum without a fluid seeping back into the reservoir?

So to fix this, I would have to fully disassemble the pump itself and remove the cylinder? I guess we're talking about the seal the bottle of the cylinder or something called the 'ucup'?

I’m not sure what type of jack we are dealing with, but the problem lies with the Pump seal, whether that is a rod/oring seal or Piston type is yet to be determined. The pump seal does the transfer from the Reservoir > Valves > Main lifting cylinder, Based off your post this is where the issue is. It more than likely wouldn’t require a full tear down.

 

[ajchien]

I do suspect it is slightly overfilled. Jack fluid is above/covering the inner cylinder when looking down into the fill hole, but I'm not experienced enough to know where the fluid level should be, what that looks like.

You could use something such as a zip tie as a dipstick. Stick it through the fill hole, hit the inner cylinder and see how much you have. A few mm above the inner cylinder (when jack is lowered) and I’d call that good.

When the jack is at its highest lift, the oil level should be above the intake port of the reservoir. In most jacks, this is the bottom most port. You won’t see it since it’s usually on the other side of the inner cylinder when peering through the fill hole, so trying to use it as a gauge of how much oil you need isn’t something anyone does.