Vacuum Pump Operation to remove air from hydraulic system

[johnchrc]

Can anyone explain or have link to site that explains the details of a vacuum pump designed to remove aire from hydraulic system? I have a procedure below but
a) not sure why only fill chambers with 3/4 full of oil before starting vacuum.
b) Why would oil pressure drop to 15 psi? Would it not increase?

PROCEDURE FOR REMOVING AIR
1.Attach a pump adapter to the upper and lower fill ports of chmaber.
a. VACUUM line from the pump goes to the downhole plug.
b. PUMP line from the pump goes to the uphole plug.
2.Fill the pump reservoir ¾ of the volume with HVI 26 Univis oil.
3.Check and confirm that the bottom valve of tank is open.
4.Check and confirm that the pressure relief valve is open.
5.Vacuum tool until no air bubbles are visible in the pump reservoir (approx. 5 minutes).
6.Shut off vacuum. Drop oil reservoir pressure to 15 psi. Start pump; pucks may expand.

Thanks for your help.

Regards,
CJ


- CJ

 

[MikeHalloran]

a) When you pull a vacuum on a reservoir in a system that has gas dissolved in liquid, or has air pockets trapped above a liquid, a lot of liquid is going to flow toward the vacuum pump, especially when it's first started. Vacuum pumps in general don't like pumping liquid; at the very least it contaminates the sealing oil in the pump. If you pull a vacuum on a reservoir that has zero headspace, you are going to be pulling straight liquid until the elastic parts of the system have shrunk in response to the vacuum.

b) The procedure only applies to the system in your combined assembly drawing/ PID/ schematic/ illustration, which carries too much information for clarity, and too little information for us to figure out what 15 psi has to do with anything. The missing lines don't help either.

The procedure references an open pressure relief valve, which in most cases should not be open, and in this case does not obviously exist in the system.

Also, the whole idea of removing air from all parts of a system, even remote parts, through the system's liquid content, using a vacuum pump, seems rather unjustifiably hopeful. The surest way that I know to remove air from a hydraulic system is to drain all the liquid, evacuate the system, and admit the new liquid while the system is still under vacuum.

Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

The 3/4 full would be to keep the rightmost reservoir top inlet opening below fluid level so air bubbles can be observed. And to keep the vacuum pump inlet above liquid level in the observation reservoir so as to not draw in liquid.

Is 15 psi 15psia, atmospheric pressure? What are the units on the vacuum gauge?

What is the device that is being evacuated?

Ted

 

[johnchrc]

That is what we do, admit fluid while under vacuum after several cycles. Then pump into and install plug.

I cant show the entire schematic but it should give you the general idea how this vacuum pump works. It is shown with one pump line and two vacuum lines. It isn't the same tool I have which uses one pump line and one vacuum line.

I just don't understand the 3/4 fill and the reduction to 15 psi when in fact it should be less. Maybe it was a typo and it was meant that you open the vacuum and let oil return back to atmospheric pressure as it back fills?

It actually makes sense to me now after realizing it was shown rigged up to another tool (which I never use the vacuum tool on to fill). I usually increase pressure to dissolve gas and bleed and most is evacuated when I bleed. Then I fill at and angle conducive to eliminating remaining air.

- CJ

 

[johnchrc]

hydtools,

Thnaks for the info on the partial fill.

The 15 psi in the oil fill may be becasue the vacuum is shut off and the pump is turned on pulling fluid from the reservoir. I'm not sure if the vacuum gauges show 0 psi as atmospheric or the actual atmospheric pressure. From the instructions I have it says to drop rservior presure by 15 psi so the vacuum would have had to be released snd closed prior to starting pump. They have a vacuum gauge on the reservoir to observe pressure chnages. The circular plate in the reservor is to force bubbles back up so they can be observed.

The tool is a downhole oil tool that is isolated from the wellbore but sees a 300F temp increase so we remove about 8% of the fluid from the chamber by positioning a piston to displace said oil. The fluid path is tortouous so air is easily trapped in certain sections of the tool.

I have come across two sets of instructions. I believe the cotrrect instructions are to fill the tool at 30 degree angle, vacuum the chamber until no air is seen, backfill by releasing vacuum and then cycle fluid through the tool to remove any other air pockets then plug the port. I would assume the tool must remain lower than the vacuum pump reservoir.

- CJ

 

[MikeHalloran]

... and the second set of instructions?


I personally would drain the entire tool by manipulating it as necessary and blowing air through, etc., then evacuate it 'dry', and then fill it by allowing the vacuum to pull the oil in, then plug it.



Mike Halloran
Pembroke Pines, FL, USA

 

[johnchrc]

Mike,

That is essentially what I am going to do. Pull a vacuum for 5 minutes and then let vacuuum backfill. Thanks for your comment.

- CJ