Thermal expansion of hydraulic fluid oils

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
jimh
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Location: Michigan, Lower Peninsula
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Thermal expansion of hydraulic fluid oils

Postby jimh » Mon Dec 16, 2019 1:43 pm

I found an interesting short discussion on the thermal expansion of hydraulic fluid oils at

https://www.q8oils.com/general-industry/hydraulic-oil-compressibility-what-is-it-and-what-are-the-risks

This article notes:

The volume of a specific hydraulic oil not only changes due to pressure changes, but also due to changes in temperature. When the temperature increases, the density of the oil decreases, leading to an increase in volume.


Another website also remarks on thermal expansion of hydraulic fluids:

http://graco.custhelp.com/app/answers/detail/a_id/110/~/thermal-expansion

What is thermal expansion and how is it caused?

Thermal expansion is caused in a sealed system by the expansion of the fluid volume due to increased temperature of the fluid.

What fluids are affected?

All fluids...are subject to thermal expansion at varying level..[such as] hydraulic oils...


On this basis, it seems that a boat steering system using hydraulic fluid should probably be vented at the helm pump as a means of allowing for some thermal expansion of the fluid volume in the steering system without an increase an the static pressure of the system.

NLA01
Posts: 172
Joined: Sat Nov 14, 2015 10:25 pm

Re: Thermal expansion of hydraulic fluid oils

Postby NLA01 » Sun Dec 22, 2019 10:46 pm

Seastar helms do have vent screw on the top of the helm for venting