Higher speeds, increased pressures, reduced reservoir size, the need for higher production output and longer fluid life, as well as environmental concerns, all play a role in the continuing trend for more durable hydraulic fluids. So you may wonder if your fluid will continue to provide the protection your system needs.
Higher working pressures lead to higher operating temperatures, which may increase the oxidation rate and thermally stress fluid. Smaller reservoirs have multiple effects. Entrained air doesn't escape, foam doesn't break up, water doesn't separate, contaminants don't settle out, and the fluid doesn't cool. Fluids are the life blood of a system. The industry must keep up with the demands on systems and fluids that keep them running.
Durability study
A fluid's anti-wear durability is essential for successful operation. One of the best ways to determine durability is to take the standard pump tests and push them to the limit — by extending their length or running them at higher temperatures or in the presence of contaminants. The goal is for the fluid to continue to protect the pump from wear over its rated service life. Our durability tests show that the premium hydraulic fluids provide the durability for long, service-free performance.
There is no industry test method to measure the effects of increased stress on fluids. Current test methods involve short-duration pump testing coupled with laboratory bench testing. In this study, we used widely accepted pump tests, including the Denison T5D vane pump, the Eaton-Vickers 35VQ25 vane pump, and the Sundstrand Series 22 piston pump tests.
Although all of these tests successfully predict wear characteristics of a fluid, they suffer from relatively short test duration or low temperature. As a result, they only measure the presence or absence of an anti-wear additive in the fluid.
We drained used oil and submitted it for evaluation in standard ASTM bench tests to determine performance retention. We used the Denison HF-0 specification bench test protocol because it evaluates most aspects of hydraulic fluid performance.
The fluids used for this study included multigrade and monograde formulations that were blended with good quality Group I base stock. The hydraulic package selected for this study was added at the recommended level. The multigrade fluid contained a shear stable viscosity modifier.
Sundstrand test — When we ran a Sundstrand piston pump test under standard conditions (180° F, 225 hr, 5000 psi, and 3100 rpm), it passed all manufacturer-established criteria. When we ran it a second time under standard conditions — but doubled the time to 450 hr — it also passed.
The Sundstrand pump test includes 1% water contamination to further stress the fluid. Even with added contamination, there was no evidence of hydrolytic instability or filter plugging problems related to water contamination.
We ran the test a third time at an elevated temperature of 250° F. Because of the higher temperature, we added no water to the test; however, all other conditions remained the same. The samples still passed the series of tests.
We concluded that the hydraulic fluid based on the premium anti-wear formulation had the durability to exceed the performance parameters of the Sundstrand piston pump without a problem.
Eaton-Vickers test — The next phase involved running an extended-length Eaton-Vickers 35VQ-25 vane pump test to determine the durability of the anti-wear formulation. We ran the test at standard test conditions of 200° F, 3000 psi, 2400 rpm, and a flow rate of 38 gpm. By increasing the time limit from the standard 50 to 1000 hr, we saw progressively more amber to dark brown varnish deposits in the reservoir as the test progressed from 500 to 1000 hr.