Counter balance valve and pressure due to thermal expansion of oil in cylinder
Counter balance valve and pressure due to thermal expansion of oil in cylinder
(OP)
Hi, I've a question regarding counter balance valves. In a typical circuit as attached but in my case the cylinder pulls downwards. Sometimes the load is stopped at intermmediate positions for long times and sometimes the pressure is needed to keep the load firmly attached to the ground.
The cylinder is under the sun and will not be operated for long times. So, If I think right, the oil in the cylinder will heat and expand. The counter balance valve will be closed because there's no pilot pressure and the stem will develop huge foce.
To avoid this I'd have to add an overpressure valve between the cylinder and the counterbalance but this valve is not that tight so pressure in the system will be lost in those cases I need pressure against the ground.
Is there a way, purely mechanical (without using pressure switches and PLC) to keep the cylinder in intermmediate positions for long times and avoid the thermal pressure?
Best regards,
The cylinder is under the sun and will not be operated for long times. So, If I think right, the oil in the cylinder will heat and expand. The counter balance valve will be closed because there's no pilot pressure and the stem will develop huge foce.
To avoid this I'd have to add an overpressure valve between the cylinder and the counterbalance but this valve is not that tight so pressure in the system will be lost in those cases I need pressure against the ground.
Is there a way, purely mechanical (without using pressure switches and PLC) to keep the cylinder in intermmediate positions for long times and avoid the thermal pressure?
Best regards,





RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
It looks like the valve has a separate over-pressure relief in it already on the piston end.
RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
If thermal expansion occurs, it will simply push the cylinder out as the rod side is open to tank.
can you provide a drawing and hydraulic schematic of what you are doing?
do not add an RV between the counterbalance and the cylinder, the counterbalance valve should be mounted as near as possible to the cylinder in case of hose failure. The counterbalance valve acts as an RV anyway.
RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
Ted
RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
Ted
RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
Ted
RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
The only way I've found so far in small cases is dimensioning everything against 160 bar of max pressure + 100 bar due to temperature. But with big cylinders is becoming a problem to size everything that big.
RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
je suis charlie
RE: Counter balance valve and pressure due to thermal expansion of oil in cylinder
It's good to consider, but matching the expansion of oil to the expansion of metal is unlikley to happen.
https://en.wikipedia.org/wiki/Thermal_expansion#Ap...
From the Wikipedia article on the topic, steel (in SI units) is 32.4 vs gasoline at 950 and glycerin at 485, though turpentine is a low of 90. Still, between 3 and 31 times the rate.
<rant>
I'd be more interested in hydraulic oil actual values, but the lack of standardized units really irritates me. Can everyone just get along with PPM-linear and PPM-volumetric? How hard is that? So tired of 0.000005 and 0.005% and 5e-5 and 50E-6 and if those aren't the same number, then that's what I'm getting to.
</rant>