Why do hydraulic control valves start leaking, drifting or sticking? Two main reasons: Contamination and Cavitation.
Contamination:
Contamination is a pretty straightforward problem. The most common situation we see is a cylinder or other component fails, sending metal shavings and other debris into the hydraulic fluid. If this contaminated hydraulic oil is then run through your valve, the metal shavings and debris are forced through your valve at high pressure. With tolerances inside a control valve at 0.0005", any scoring of the spools causes problems. If a spool is damaged slightly, the constant flow of oil at high pressure, over time, can make things even worse.
Fixing Valves that Fail Due to Contamination:
We can repair most scoring due to contamination on hydraulic valve spools. The deeper the scoring, the more grinding and chrome buildup (and cost) it will take to bring your spools back up to tolerances.
Preventing Contamination:
You can prevent contamination by installing proper filters on your hydraulic system and changing them every 2 months (or more with heavy usage or extreme conditions). You should also replace your hydraulic oil yearly. If it is cost prohibitive to drain your fluid yearly, we can run a test on your hydraulic oil to detect the level of contamination.
Cavitation:
Cavitation is a more interesting problem. Cavitation happens when the demand for oil inside a hydraulic system exceeds the available supply of oil. When this happens, a vaccum is created inside your system. If this vaccum is strong enough, your hydraulic oil starts turning from a liquid into a vapor. When these little bubbles of hydraulic oil vapor are compressed... they implode. When these bubbles implode, they wreck havoc on the inside of your components.
Fixing Valves that Fail Due to Cavitation:
Akron Hydraulic can repair spools that have been eroded by cavitation. We do this with hard chroming and precision grinding. This process can usually save you $1000's versus repalcement with new.
We can also repair some valve body problems including washed out lands. See these before and after pictures of valve body lands we have repaired. Click on this link and you can read more about fixing washed out lands in a control valve.
Washed Out Land Before
Washed Out Land After Repair
Valve repair fixes a SYMPTOM of cavitation, not the PROBLEM of cavitation. If you like, we can assist with fixing your hydraulic system so that cavitation doesn't occur in the first place.
Preventing Cavitation:
Cavitation can be prevented by a well designed hydraulic system that includes working load control and anti-cavitation valves.
Dan Root | tagged 
