From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: Water pumps  Somebody STOP me!
To: flyrotary
Date: Thu, 09 Oct 2003 18:32:37 -0400
Message-ID: <web-2630692@logan.com>
In-Reply-To: <20031009151509.ONAU1644.fed1mtao04.cox.net@smtp.west.cox.net>
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Posted for Dale Rogers <rogersda@cox.net>:


Tracy Crook <lors01@msn.com> wrote:

>   I bring this up occasionally to either:
> 
>   A.  Dispell a popular myth
> 
>   or 
> 
>   B.  Eliminate a big misunderstanding on my own part.
> 
>   I'll accept either outcome but so far no one has addressed the issue. 
> Based on everything I (think I ) know about pumps:
> 
>   Assumeing a constant pump speed, when the thermostat closes and head 
>pressure goes up,  power required to drive the waterpump does NOT go up.  It 
>actually goes DOWN.  Reason:  There is less mass being accelerated (energy) at 
>lower flow rates.  In the extream example  (zero flow) the same water in the 
>pump housing is being spun around at a constant velocity which requires no 
>energy.  Of course there are losses in the pump so the energy consumed is not 
>zero.
> 
>   This argument applies ONLY to centrifugal pumps (of which automotive 
>waterpumps are an example) and not positive displacement types (like oil 
>pumps).
> 
>   OK, somebody shoot this argument down and educate me.

    I'll admit I don't have all the science involved fully integrated; but I 
would like to point out that a fluid coupling (e.g. auto trans.), which is a 
type of centrifugal pump, appears to display just the opposite behavior.  

regards,
Dale