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Single Acting Vertical Jack

Single Acting Vertical Jack

(OP)
Here is an interesting scenario just looking for an explanation.

I just recently had brought to my attention a scenario with a hydraulic elevator.

The elevator cab was suspended from above and the piston was disconnected from the car. The shutoff valve was closed at the tank with hydraulic fluid and pressure still on the system and left in this state overnight. Normal operating pressure is approximately 400psi.
The next day the piston had descended 55" with oil coming out of the gland packing on the porthead. But the tank had lost 4" of oil which my calculation works out to 32 liters of oil of oil loss. The control valve is located 12" above the oil level, the piston is 3.5" in diameter. The porthead is located approximately 5 feet above the oil level in the tank.

The question at hand is what had caused the oil level to decrease in the tank with the ball valve closed and with the out put on the control valve located above the oil level, as well as the port head located 5' above the oil level?

Any explanation and technical explanation would be greatly appreciated.
Thank you.

RE: Single Acting Vertical Jack

What's a porthead? Even Google isn't finding the term.

Thermal expansion may account for a portion of this.

It's not clear if the cab was disconnected and separately suspended how there was pressure still on the system, besides the rod weight, which should be less than 400psi. Is there some diagram of all the joints and a free-body diagram showing how the loads are applied?

RE: Single Acting Vertical Jack

(OP)
Cylinder head - port head; sorry trade term.

The only pressure that would be on the system is what was used to get the cab to the position it was suspended at then the shutoff valve closed. There is seven 90 degree joints in the system on 2.5" piping.

This is a generic layout.
Example of the style pump/valve system.

RE: Single Acting Vertical Jack

Maybe your level measurement in the tank is not good. You would have a bulkhead that is not waterproof and a visual level on the side or the oil is higher when the test starts. Then with time the oil passes to the other side of the partition ?????

RE: Single Acting Vertical Jack

(OP)
That's where it gets weird, the cylinder was pulled and tested with no indication of bulkhead issues, the oil level measurement was precise. The only thing i can think of is some-way the weight of the piston had cause a suction affect if the possibility the shut off valve isn't fully sealed.

RE: Single Acting Vertical Jack

do you have a hydraulic circuit/schematic?

RE: Single Acting Vertical Jack

For a cylinder connected in double effect when the rod comes out: the level in the tank drops. Since the bottom section is larger than the annular section.

RE: Single Acting Vertical Jack

(OP)
Single acting/closed system and piston dropped but oil level in tank dropped as well, no holes in cylinder or bulkhead. No power on system and ball valve closed at tank.

RE: Single Acting Vertical Jack

If the volume lost is not in external leakage, I see only a variation of the volume of the fluid.

The volume increases by increasing temperature: for normally aerated oil it is 1% by volume for 15 ° C.

The volume could decrease by deaeration. If you have an air intake in the circuit and given your low working pressure you can have an emulsion in the cylinder and in the tank. This is very unlikely because the system would be noisy and you would notice an elasticity in the operation of the cylinder as if you had a pneumatic cylinder. In the absence of all the data of the problem why not this wacky assumption?

A volume of normally aerated fluid also decreases when the pressure increases: 1% by volume for 150 bar.

It is considered that a metal enclosure (tank, cylinder, pipe) has a very low temperature or pressure expansion compared to oil.

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