Springs and Additives

[MolaKule]

Subject: Hydraulic System and Fluid additives.

Setup: A hydraulic system has a 3 GPM pump that will be used to develop sufficient pressure to move an 8000 lb. load, using a cylinder with a round 10 Sq. inch piston face. So to move the load, the system pressure needs to be > or = 800 psi. However, at the end of piston travel when the load is no longer moving, the pressure will rise.

We want to keep the system pressure at or less than 1000 psi in order to not blow the seals in the various system components. Therefore, we will use a pressure 'relief' valve tapped into the high pressure line to keep the pressure from exceeding 1000 psi.

A spring in a simple hydraulic pressure 'relief' valve below uses its 'spring rate' to set the maximum pressure in the hydraulic system. When the system pressure gets to the 'cracking' point of about 998 psi, the pressure P will exceed the spring force and the cup (blue) will move to the right to allow fluid to be diverted back to the accumulator tank, thus keeping the pressure from exceeding 1000 psi.

Question: Due to the possibility of some moisture coming in through the breather and getting into the hydraulic fluid, we might be tempted to use a valve body and spring of stainless steel to avert corrosion and rusting.

But a standard steel spring and housing will suffice if we incorporate what additives into the base oil?

This question is open to all, but lets give it a day or two for non-engineering BITOG members to research the question and respond before the engineers pile-in.

 

[TMoto]

Without doing any Googling, I'm going to guess rust inhibitors. Is that too generic of an answer?

 

[wwillson]

I would say anti-oxidants

 

[wpod]

Corrosion inhibitors

 

[jurko]

Zn and P and also potassium hydroxide which fight acids and therefore corrosion?

 

[Jetronic]

I would have gone with anti-oxidants too

 

[MolaKule]

Thanks to all who gave participated and gave answers.

Since the hydraulic piston, the accumulator tank, and the bypass valve would all be likely made of steel, one of the components in the DI additive package should be a rust inhibitor in case we have moisture intrusion, such as a sodium sulfonate, a Dodecenylsuccinic acid, or a similar component.

A corrosion inhibitor should be included if there are other metal alloys present in the system, and a Multi-Functional component such as a zinc dinonylnaphthalene could serve as a Rust Inhibitor, Demulsifier, and a Corrosion Inhibitor to cover all the bases.

If an anti-wear component such as ZDDP is allowed in the hydraulic oil, it can also serve as the anti-oxidant. If it is not allowed, an amine phosphate component could serve as this agent.

 

[DriveHard]

I was so excited to answer a hydraulic system question until you twisted it into an oil question ;-)

 

[wpod]

I have worked on many old forklifts that were perfectly serviceable but the owners never changed the hydraulic fluids and there is condensation and the hydraulic cylinders would corrode and wear out the seals and with the corroded rough surface the cylinders would have to be replaced.

 

[RDMgr]

FYI-Most hydraulic oils use a hydraulic oil adpack and not a DI or dispersant-inhibitor adpack. These are typically used for engine oil. There are a few exceptions.

Most HO adpacks contain AW, oxidation inhibitor, anti-foam, corrosion and rust inhibitors. Sometimes a VI Improver is used. Normally there are no dispersants.