[Healeys] oil pressure relief valve - but if old ...

[Robert Blair]

Paul, Jim, Michael, Yes - true for a good 60 lb spring/seating condition.

BUT, if the spring is weak [old, short, constricted] and is
relieving/compressing at say 30 lbs, then the internal pressure will not
overcome the relief valve and the guage and bearings will not see pressure in
excess of 30 lbs - a weak spring acts like a 'big leak' in the system that the
pump cannot overcome.  Just like a worn bearing. If you 'plug' the leak [ie
get the spring to stay closed until 60 lbs - ie have a good spring/seating]
then the system will see internal pressure up to 60 lbs cold as delivered by
the pump.  When hot, 60lbs is not achieved because the oil viscosity decreases
with temperature [reducing flow resistance and therefore pressure, and 60lbs
is not achievable by the pump against the lower resistance of the complete
system - the good spring remains closed as pressure within the system is then
below 60 lbs.  When hot, pressure is limited by the condition of the bearings,
rocker etc to 'resist' oil flow from the pump.  Lower flow
 rate results in higher pressure.  Higher flow rate results in lower pressure.

So check your springs ......

Robert N. Blair  Yellow 65BJ8  RNBmail at yahoo.com
 



--- On Tue, 9/28/10, Michael Salter <msalter at precisionsportscar.com> wrote:

> From: Michael Salter <msalter at precisionsportscar.com>
> Subject: Re: [Healeys] oil pressure relief valve
> To: healeymanjim at hansencc.net
> Cc: "healeys at autox.team.net" <healeys at autox.team.net>
> Date: Tuesday, September 28, 2010, 9:18 AM
> You are absolutely correct!!
> There is NO fallacy in your thinking.
>
> Michael Salter
>
> On Tue, Sep 28, 2010 at 11:42 AM, <healeymanjim at hansencc.net>
> wrote:
>
> > i am having trouble understanding how increasing the
> spring strength in the
> > oil pressure relief valve will increase oil
> pressure.  this spring is
> > calibrated to keep the oil pressure in the engine to
> below aprrox 60 psi.
> >  when the oil is cold and the pressure is above
> that, the spring is
> > compressed and excess oil returns to the sump. 
> once the oil heats up enough
> > to allow the pressure to decrease below 60 psi the
> relief valve closes,
> > never to enter the equation again.  increasing
> the spring strength would
> > only cause the relief valve to come off the seat at a
> higher pressure, i.e.,
> > 70 psi with cold oil.  i cannot see where
> increasing the strength of the
> > spring would do anything to increase the pressure of
> hot oil, say from 35 to
> > 45 psi.  where is the fallacy in my
> thinking?   hjim