Re: IML: Re : pressure vs volume

["Roger Casagrande" <rdc2382@xxxxxxxxxxx>]

Any fluid pump will produce a maximum pressure level by design and the power 
source capability. The flow at a given pressure delivered to the system 
(through the engine) is dependent on the system flow resistance (ie. engine 
clearances and flow passages). The maximum pressure is at zero flow, and the 
pressure reduces as the flow rate increases. So having a too high pressure 
reading may be bad, which indicates blocked oil flow. Having too low a 
pressure reading may be a sign of increased internal pump wear or leakage. 
That's why there is a specified pressure range from the factory that 
indicates the lubrication system is operating properly.

Roger
'55 Newport


----- Original Message ----- 
From: "mike and linda sutton" <mikanlin62@xxxxxxxxxxx>
To: <mailing-list@xxxxxxxxxxxxxxxx>
Sent: Friday, March 30, 2007 9:08 PM
Subject: IML: Re : pressure vs volume


> This comes up all the time in various forms. Follow along....your oil pump 
> is a positive displacement pump meaning it can move a set amount of oil 
> each time it rotates, whether it is a spur gear style or a rotor style 
> like Chrysler uses.  So for EXAMPLE, if it can displace an ounce of oil 
> for each revolution of the pump it will move 1000 ounces at 1000 engine 
> rpm. Now, if the various clearances in the engine bearings, crankshaft, 
> connecting rods, lifters, pushrods, let less oil past them than the pump 
> can move you will get pressure.
>
> If this doesnt seem clear, remember that we are talking FLOW here, and 
> resistance to FLOW causes PRESSURE. Dont think so..go turn on the garden 
> hose and let it run, youll see flow. Then put your finger over the end of 
> the hose and close it off about half way, you reduce the flow but increase 
> the pressure.  Its not quite the same as the kind of flow vs pressure you 
> see in hydraulics where there isnt any leakage desired because in an 
> engine its a given that you will have oil leaking past the various 
> clearances in the engine, thats how it is designed. The oil cools as well 
> as lubricates.
>
> This is also why as an engine wears out the pressure will drop, because 
> the clearances get larger as the bearings and other surfaces wear. Since 
> the pump can still only move a set amount of oil, whatever that amount is, 
> the resistance to the flow of the oil lessens and the pressure drops 
> accordingly.
>
> Use a high volume pump as opposed to a high pressure pump. The only 
> difference between standard and high pressure is the relief spring and you 
> dont need higher pressure anyway. A high volume pump will give you more 
> than enough oil flow to create  good oil pressure.
>
> Mikey
> 62 Crown Coupe
>
>
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