[modeleng] Re: Oil Clacks

Gents,

For my two penny worth I have only ever fitted one clack in the oil delievry 
system and to date don't seem to have problems.  I also believe that most 
locos in our sizes use too much oil anyway.

Regards IDP

"Life should NOT be a journey to the grave with the intention of arriving
safely in an attractive and well preserved body, but rather to skid in
sideways, Champagne in one hand - strawberries in the other,
body thoroughly used up, totally worn out and screaming WOO HOO - What a
Ride!"

"Never drive faster than your gaurdian angel can fly"

Priest & Sons Model Engineers
http://www.kinvermes.pwp.blueyonder.co.uk/p1.htm

----- Original Message ----- 
From: "John Pagett" <john_pagett@xxxxxxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Monday, June 05, 2006 10:33 PM
Subject: [modeleng] Re: Oil Clacks


Barry,

I think it comes down to leakage volume. The amount of oil pushed through a
check valve per stroke of the arm (not per revolution of the shaft
"downstream" of the ratchet/clutch) must be very small. If there was any
leakage it would probably get pushed back during the return stroke of the
lubricator arm. A second check valve adds insurance in case something
foreign gets under the ball.

On the other hand, you'd need a much larger leak before this effect showed
up in the water system BUT you usually do have a clack on the boiler and two
non-return valves in the pump, so the boiler clack and the pump delivery
check valve are in series (although the by-pass is usually tee'd off between
the two). It's true that injectors don't usually have two non-return valves,
maybe this is to keep the delivery more free, though I'm not sure if that's
the case.

At the risk of teaching grannies to suck eggs, it's always a good idea to
have a check valve close to a pump so that if air ever gets into the system
the "compression ratio" should be high enough to push the air through the
system, rather than uselessly sqeezing it up to something less than boiler
pressure and then letting it relax again as the ram comes back. I believe
that some cheap air compressors rely on this effect to limit the maximum
system pressure.

Members of the list are free to disagree!

JohnP

----- Original Message ----- 
From: "Barrie Purslow" <bpduo@xxxxxxxxxxxxx>
To: "Model Engineering List" <modeleng@xxxxxxxxxxxxx>
Sent: Monday, June 05, 2006 10:09 PM
Subject: [modeleng] Oil Clacks


I have always been told that we fit two clacks in the oil delivery from a
mechanical lubricator as "extra security" against water getting into the oil
reservoir. But, if this is the case, why don't we fit two clacks in boiler
feed pipes?
Could it be that the real reason we fit two clacks in the oil supply is that
the clack at the pump outlet is to enable the pump to work and the clack at
the other end of the delivery pipe is to prevent the pipe from emptying
whilst the locomotive is stationary?? (This would mean the cylinders would
be starved of oil when the engine first starts until sufficient running has
been done to fill the pipe).
Barrie Purslow
Warrington U.K.
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