Removing the oil pressure relief valve

[wilf]

Paul, We went out for a little jaunt in Buttercup today, and I closely observed the OPG during start and run.

Mine too is pretty unresponsive to small throttle blips when cold. It really only moves upward from the cold fast idle 50ish psi once you get 2500 rpm or more on for more than about 3 to 5 seconds.

Slightly quicker to respond once it is hot (when idle psi drops to about 35), but still by no means rapid.

You are welcome to pop round and see how mine behaves. Or misbehaves, depending on your viewpoint.

[paulbell6]

Hi Wilf, that sounds like a damn fine idea, it would be nice to see another Stag and get to meet someone from the forum. I am out of the country over the next week or so but if the offer still stands when I get back I will drop you a pm and we could make some arrangements.

Many thanks

Paul

[wilf]

OK. I'll await your PM.

[Paul Roberts]

Paul, We went out for a little jaunt in Buttercup today, and I closely observed the OPG during start and run.

Mine too is pretty unresponsive to small throttle blips when cold. It really only moves upward from the cold fast idle 50ish psi once you get 2500 rpm or more on for more than about 3 to 5 seconds.

Slightly quicker to respond once it is hot (when idle psi drops to about 35), but still by no means rapid.

You are welcome to pop round and see how mine behaves. Or misbehaves, depending on your viewpoint.

Only just picked up this thread.

OK, let me throw this observation into the mix based upon my time spent designing meter-provers for the oil industry (albeit nearly forty years ago.)

In a (relatively) complex hydraulic circuit - such as a vehicle engine - where pipes and oilways are of a differing diameter and length, etc., the oil will always try to take the line of least resistance. For instance if an oil pipe fractured or came off the system you would not be at all suprised to see the oil all over the floor and your pressure-gauge reading zero.

Oil viscosity, which is temperature sensitive, also plays a part in this equation - cold thick oil takes longer to flow along a pipe than hot thin oil under the same pressure and a bigger pipe will permit more oil to flow than a small one under the same conditions.

Now, your pressure-gauge pipe is quite a small diameter and quite long; the oil in the engine system is dynamic, not static, and therefore much happier to squirt around the bigger tubes of the engine before it can be bothered to go to the gauge. Imagine that your gauge pipe was blocked, for some reason, the oil would happily continue to go down all the other routes regardless. This accounts for the time lag at the gauge. Eventually, however, if there are no major holes in the system and enough time is given, the overall pressure will equalise throughout the circuit - including at the gauge. The flow-rates, however, will still differ in different bits of the circuit due to the different cross sectional areas of the oilways.

Does any of that make any sense???

TBO

[wilf]

Does to me, hence my preference for air in the line to the gauge, rather than cold, viscous oil.

[paulbell6]

Hi TBO, what you say makes perfect sense. I think sometimes you can get too wrapped up in a problem and forget to take a step back to properly analyse what is actually happening. Your comments reflect that perfectly. The Stag of course was never originally fitted with an Oil pressure gauge and so maybe the aftermarket design attachments don't quite suit the system. I think having xtracted lots of info from the very knowledgable chappies on here, that I am now happier with the situation I find myself in, I will just have to take my eyes off the gauge a bit more.

Regards. Paul

[flying farmer]

I would take one of those washers out, first time I did it I put in two and the pressure went off the gauge ruining it. Recently put one washer behind the spring on the Stag engined TR, lifted hot pressure from just under 40 to just over 50, idle unchanged at about 30.

The gauge on the TR used to replace the old one is also slow responding considering they are both smiths gauges using the same pipe, I suspect the new gauge has a restrictor in it somewhere

Neil

[stag157.7]

After reading this thread
I have a headache
know we now why its nicknamed
the worry gauge


alan

[paulbell6]

Hi Neil, yep, when I have the chance over the next week or so I will definitely be removing one of the washers.

Regards. Paul