[Vwdiesel] PV=nRT and Hydraulics

[James Hansen]

Dennis sez:
leakage in the pump equates to no work being done on the leakage.
READ: no pressure built up = no heat is created.
________

Friction. Fluid under pressure moving through small space has significant
boundary layer friction.  SIGNIFICANT. Shoot some high pressure oil through
a small orfice in a line, downstream of the orfice is hot. Really hot. Fluid
leakage in a pump is going from an area of high pressure to one of low
pressure via a small space.  How does this differ from flow through an
orfice?
An anecdote from the crainial archives... Logsplitter (forget which one)
manufacturer in the eighties uses a plastic tank for hydraulic oil. Small
orfice in a bleed line that returns a tiny portion of the oil that is at
system pressure (1200psi) back to the tank to help warm the oil in winter.
Good idea, as the cold oil is too thick to pump effectively in cold of
winter. Trick is, if the unit is left to idle in summer, the tank melts
after a bit... good idea that plastic tank.
But point is,  oil at pressure flowing through a small space makes a ton of
heat. THis is fact. To locate a hydraulic cylinder that has a leaking
internal piston seal in a multiple cylinder circuit, you dead end the system
(put all the  cylinders to one end), leave the pressure on so it sees the
system relief pressure, and in under a minute, you cannot hold your hand on
the cylinder it gets so hot. The oil is doing work, it is heating.
-James



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