Brent,
Yes. I'll see if I can find that ring (probably near my big ball of
string) and take another picture. It was smooth and tapered to a small
diameter at its thinnest point. It was either damaged at pump build or the
ring originally had a material fault. I chased so many
internal leak situations until I couldn't fix them completely
(eventually replaced both the pump and the dump valve). Also, the pump
must have been assembled with a air-driven lug-nut wrench because it took an
extension on my "normal" wrenches to break the end nuts free.
Your comment on the symmetric shuttle makes sense and explains why the
very small reservoir on the older pumps was adequate.
The problem with completely flushing the gear actuators would be the
extra work to remove the retraction stops so that the piston reaches the
physical end of the cylinder and all of the fluid on that side is
expelled. When I rebuilt main actuators I was surprised to see blackened
fluid at the retraction end along with visible residue from o-ring
deterioration/wear (your use of "silt" was a very good
description). Of course that wear could have come from other contamination
causing the wear in the first place. I don't know about how others did it
but I was so very careful to keep everything clean as it was assembled and
built. But, this was not done in a white room and I did occasionally have
eye irritation. Maybe since I did so many rebuilds and replaces (including
the pump) I eventually "flushed" the system.
Since I was such a mushroom (kept in the dark, etc.) when I was a lonely
garage-located slow-builder back in the early 90's, I could only do things that
then were reasonable to me - thus repeating so many problems already solved by
others earlier in the century. Alas, where was the internet when I needed
it?
Scott
In a message dated 11/7/2007 2:12:34 P.M. Central Standard Time,
brent@regandesigns.com writes:
Tough to
tell from the picture but, because the seat is static it is unlikely that the
O-ring is "worn". It does look like the O-ring was "bitten" during
installation. Part of the O-ring was sheared off when the seat was pushed past
the step in the bore. This can be avoided by inspecting the bore for burrs
(and removing them), using an assembly lubricant (like Vaseline) and carefully
assembling the parts.
I am assuming that the other difference with the
symmetrical shuttle is an absence of a central vent port. Without the port the
system would be slow to self bleed any air in the circuit. The pumps are
valved such that there is no circulation through the reservoir. You could loop
the system with a line and remove the reservoir without affecting flow.
Reservoir flow only occurs with tidal flow due to cylinder rod volume, fluid /
air compression and system bulk modulus.
This "recirculating" design
means that any system contamination is trapped in the circuit without much
chance to get into the reservoir. Changing the fluid does nothing to remove
contamination, moisture or debris from the circuit. Hydraulic maintenance
should therefore involve flushing the system by disconnecting lines,
exercising the cylinders and running the pump.
Internal port to port
leaks are most commonly caused by contamination in the system. Metal chips,
moisture, sanding dust, dirt etc. all spell death for the system. If
contamination gets to the pump it turns the pump into a contamination
generator. A tight, leak free system will only stay that way if it is very
clean. I used to instruct the technicians that were assembling the servo
hydraulic tele-manipulators that I designed that the system would tolerate
contamination as well as their eyes do. We had 3 micron filters in the supply
line and even with that the servo valves would "silt up" during fixed flow
tests.