Originally Posted by ABN_CBT_ENGR
Originally Posted by TravlinTech
The directional valve is a 120VAC pilot controlled valve with spring centered neutral. Gauges indicate bypass at the spool resulting in drift, off of position. Manufacturer of the directional valve is Rexroth-Size 32.
The directional valve in service with the 22/18/12 had visible scoring on the spool and bore of the valve. Replacement of the valve, system cleaning and fluid change, with 15/11/6, resolved the problem. The remaining concern is the VI, of the new fluid, tested 18.9% below what was specified in the product TD.
Something mechanical isn't right here and it doesn't have anything to do with the fluid.
Rex will tell you their valves bypass at the spool as part of the design so maybe that is a part of it and can account for drift too
Scoring has a lot of causes and particle count is one of the lower ones on the list. How did you eliminate machining tolerance, thermal expansion, seal ring degradation resulting in cocking, pulsations, other fluid properties such as temp and chemical reactance?
If you say resolved the problem then why is it still there?
Seriously, some of your statements are somewhat disjointed and confusing as they don't follow a common theme.
Nothing you have related as of yet points exclusively as a fluid related problem as the primary root cause and I'm not entirely certain of the exact failure modes you are experiencing.
What are the undesirable physical actions you are experiencing and under what operating conditions and I'm sure people here can assist
From analysis, fluid worse than 15/13/11 causes scoring of the spool resulting in bypass as evidenced by gauge placement at appropriate ports in the circuit. One example would be 1 inch of drift on a 10 inch cylinder in 19/14 fluid and with a directional valve with scoring on the spool compared to no drift with 15/11/6 fluid with a new directional valve with no scoring on the spool. When an inspected valve was installed, it had no scoring, 2 day later the drift began and scoring was found on the spool. With clean fluid this does not occur but with 20/19/14 fluid it does.
The drift problem is resolved after the fluid change, cleaning, valve change and pre filtering of the new fluid. The problem remaining is the new fluid has 18.9% lower VI than specified by the manufacturer and provided to the end user.
From my perspective the fluid is the common denominator, from the beginning.
A 3500 hour, 15/13/11, fluid oxidized and created varnish at approximately 5000 hours resulting in drift, understandable. The end user was instructed that a fluid change was required in addition to directional valve replacement.
The valve was replaced, but the fluid change could not be scheduled for 2 months due to production needs.
A different fluid, with purported improved specifications, was installed preceded by a 48 hour flush. No malfunctions were observed. The drift can be easily observed visually and through monitoring I/O. The drift reoccurred three weeks after the fluid change. The end-user changed the directional valve with drift re-occurring in 2-3 days. Analysis found the fluid to be 20/19/14 not 17/15/* as specified, the DI was also deficient.
At the site, cylinder bypass was once again ruled out and the spool was found to be bound at neutral due to varnish, in addition to visable scoring. The valve and spool was cleaned in in flush mix in a heated ultra sonic tank. This resolved the binding and the drift was slightly slower. The fluid was kidney filtered and was scheduled to be changed to a third fluid with flush, cleaning and inspection.
Having prior knowledge the third fluid was 20/17/15, filtration was planned prior to transfer to the reservoir. This was completed, the system flushed, cleaned, inspected, the directional valve was replaced and the equipment functioned and is still functioning properly. Analysis indicated as noted in the first addendum to the original post. The main disappointment was VI 18.9% lower than specified by a ISO 9001 manufacturer.
The undesirables are cylinder drift when in a neutral hold position with maximum rod end pressure.
My original question was if kidney filtration alters the VII or DI components. Filtration via a Parker cart with 10 & 40 filters, typically for 12 hours. The equipment filter is bypass filtration though a 6 or 10 micron spin on filter.
Thank you