Re: Snowplow truck hydr. problem

Posted by jdemaris on December 07, 2006 at 06:08:00 from (69.67.230.233):

In Reply to: Snowplow truck hydr. problem posted by Roy Suomi on December 06, 2006 at 16:46:41:

What Mr.Schwiebert stated is correct. Regardless if the gear pump is a Webster Electric, Cessna, Parker, etc. - the external shaft seal is not intended to seal against pressure oil - only residual. And - with all the Parker gear pumps, I don't believe they ever made one rated at lower than 2500 PSI contant duty - and most commercial rated pumps are rated at 4000 PSI or more - constant duty.
Anytime a gear pump starts pushing out the seal - it is an indicator of #1 a worn out pump, or #2 the working pressure exceeds the rated PSI limit.
Both situations are, more-or-less, the same - since a when a pump wears, it's working PSI limit decreases. The high pressure sealing is supposed to be done by the smooth face of the gear against the pump housing or thrust plate. On some model pumps, there is a replaceable thrust plate sealed by o-rings or a spider gasket - and on other pumps - nothing is replaceable. So, it possible to exceed the rated pressure and blow a gasket - which can be fixed. It's also common for the pump to get scored, bushings wear, etc. - and the pump is unrepairable junk.
Some Parker gear pumps have internal pressure relief valves.

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