Subject: Water pump test.
From: ACRE
Date: 7/14/2003, 2:35 PM



"In theory" and as I understand your system, ANY airspace, capped or not

in

your stand pipe on the pressure side of the valve will distort the
performance.

The standpipe should be on the suction side of the valve, with no air at

all

in the pressure side.

Bob Darrah


Why?


Not that there is much airspace. My guess is its less than one cubic inch.

Paul Lamar



In order to bring a cubic inch of captive air to, say for example, to 15
psig, you have to compress it by 1/2 cubic inch.  In your system, in order
to do that, you have to get 1/2 cubic inch of water from someplace.  In your
test rig, the only place you can get it is from the intake side, and that
would starve the intake side unless you put a stand pipe on that side to
supply the necessary water.  You will not get any useful pressure readings
with your setup.

I done told Orville and I done told Wilber it would never get off the
ground.

Bob Darrah


I totally disagree this is a closed loop system. THE STAND PIPE IS SEALED.
The stand pipe does NOT add water. What ever water is in the system is in the
system. Now the one cubic inch of air is probably mixed up with the one
gallon of water that is in this test system.

Paul Lamar


I think part of the confusion is the stand pipe is not a stand pipe in the true
definition of the term. Nor does it work like a true stand pipe. For a stand pipe
to work as a stand pipe it must be vented to the atmosphere. In this case it is
NOT vented.  It is just a branch and a way of getting water in the closed
loop system initially.

BTW if you would like to verify my results here is a good place to locate
the pressure gages. Drill with a 11/16th drill and tap with a 1/4 NPT.

I used McMaster Carr 2" gage part 4004K4 0-30 psi +/- for the pump inlet side
and 2" gage part number 3846K13 0-30 psi for the pump outlet and block outlet.




Paul,

I see where Bob Darrah is coming from, and you are both right. However, with your current setup, you can only get meaningful data when you pressurize the system such that the inlet pressure guage never goes negative. As long as the total system is pressurized, then you can read the inlet and outlet pressure readings and get the delta-P. Alternatively, get a negative reading pressure guage for the inlet.

If I recall your first run, (unpressurized), the pressure was very low, for the reason that Bob stated, since the air column could compress, you couldn't raise the pressure on thepump outlet. What was happening was the inlet pressure was going to about -12 psi.  After you pressurized the system, then you could read both gauges, and got a delta-P of 12 psi.

Several items to consider in any of these tests:




1. The pressure generated by the pump is a function of the RPM ( I believe it is a function of the square of the RPM)




2. When dead-headed (zero flow) you get the maximum available pressure.




3. When you allow flow, the pump (at a given RPM) generates the same pressure as at zero flow, MINUS internal losses -- the internal pressure drop in the pump.  So with your tests, the flow goes to a high value because there is little restriction, however the delta-P across the pump is essentially the same (minus the internal losses).  That means that the balance of the system requires ~75 GPM to get the offsetting pressure drop.



4. When you put other components in the system (engine block and radiator), the delta-P across the pump will *remain the same* at a given rpm, but the flow will drop off dramatically due to the pressure restrictions of the flow through the balance of the system.

If you could measure several points of dead-head pressure as a function of RPM, say 1000, 2000, 3000, 4000, 5000 that would be really useful information.

Bill Schertz
KIS Cruiser # 4045



I filled that "stand pipe" to the top. There may have been a quarter inch of air in there.
In fact the last time the pressure went up one or two psi as I screwed the cap down.
There is no column of air. The gage will be here any minute. I won't get to
test again until Wednesday as tomorrow is Robins birthday.

Lower RPM's are not of much interest to us but I will make another run
at a lower RPM.

Paul Lamar
 
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