[Healeys] Oil Pumps

WILLIAM B LAWRENCE ynotink at msn.com
Wed Jan 1 12:23:50 MST 2020

Oil pumps, vane, rotary and gear type are all positive displacement devices, meaning that they will continue to build pressure against resistance to the point where something breaks. That is why they are all equipped with a bypass valve which limits the amount of pressure in the system. The amount of stress on the geardtrain is directly proportional to the pressure developed. I'm not sure if the problems related to the rotary type pumps is a result of the stress of driving the pump or to the larger pressure pulses (vibration) that are inherent in the design.

The manufacturer selects the bypass valve and spring assembly that will keep the pressure within a safe range while protecting the drive system from over stress. The four cylinder engines are supposed to run at a maximum of 50-55 PSI, the sixes somewhat lower, and it is the bypass valve that maintains that pressure even though the pump itself is capable of much higher pressures if it encounters excessive resistance.

Viscosity change in the oil when at higher temperatures will reduce pressure by reducing the resistance of the oil circulating through the various clearances in the engine. As the engine wears these clearances will increase thus reducing resistance and dropping oil pressure. Oil pressure alone is not as important as is a constant flow of oil to all components combined with the film strength of a good quality oil.

Bill Lawrence
BN1 #554
From: Healeys <healeys-bounces at autox.team.net> on behalf of Kees Oudesluijs <coudesluijs at chello.nl>
Sent: Wednesday, January 1, 2020 6:37 PM
To: healeys at autox.team.net <healeys at autox.team.net>
Subject: Re: [Healeys] Oil Pumps

Absolutely correct. There may be theoretically a tiny difference,
immeasurable probably, caused by the efficiency of the various pumps.

Kees Oudesluijs

Op 1-1-2020 om 19:24 schreef Bob Spidell:
> I'm not a fluid dynamicist, but wouldn't, say, 45psi from either a
> vane/rotor type pump put the same load on the cam gear and driveshaft
> as 45psi from a gear-type pump, all other factors--oil viscosity,
> etc.--being equal?  Or, is there some other factor(s) at play?  Do the
> gear-type pumps produce lower pressure (seems to me that's the only
> way they'd reduce the load on the gears and the cam thrust plate)?
> Bob
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