Here is a picture of the test set up. It is a closed loop system
with a ball valve using 1-1/2 ID pipe through out.
Well as I suspected there are some significant differences in the
closed loop system compared to the open loop system.
Kind of blew me away when I saw 40 GPM on the flow
meter with a wide open valve at only 2000 pump RPM.
With the valve partial closed (fully closed is 90 degrees)
the flows are as follows.
25 GPM and 15 GPM at 2000 pump RPM's see the pictures below.
The flow is a very sensitive function of the total restriction
in the system. At low RPM's small increases in restriction will
generate rapid losses in total flow. Pressure increases are
minimal. The highest pressure I have seen on the outlet of
the pump so far is about 3 psi.
At 4200 pump RPM wide open it pegged the flow meter at well over 75 GPM.
I adjusted the valve partially closed for 75 GPM at 4200 pump RPM and the
30
amp 110 volt circuit breaker blew in about 30 seconds.
I need to borrow a more powerful mill. No doubt about it these pumps
suck the HP. The pump get quite warm on only a few seconds of running.
Paul Lamar
William wrote:
Shouldnt the stand pipe be on the suction side of the pump?
Bill
Why?
Went back today after the RTV pump gasket had a chance to cure.
I changed to a lower ratio on the mill step pulley system and wonders
of wonders the pump ran at 4200 RPM without blowing the circuit breaker.
Exactly the same pump RPM with the higher ratio. Apparently
the mill motor was overloaded and slowed down by that much.
I could now shut off the system completely. 4200 RPM
GPM
Flow Press psi Valve
0 3 closed
25 1
35 0
45 0
55 0
65 0
75 0
off scale 0 wide open
I have no idea what the negative pressure was on the inlet side
of the pump as the gage was bottomed out. Will get a +/-
gage next week and rerun this test.
I then pressurize the system to 15 psi using the air compressor.
GPM
Flow Press psi Valve
0 18_17_6 closed
25 18_16_6
35 17_15_6
45 15_13_6
55 15_13_6
65 15_13_6
75 15_13_6
off scale 15_13_6 wide open.
Stoped: 14_14_14 psi. wide open.
Pressures are in order: pump outlet, after flow meter,
inlet side of the pump.
As you can see in a closed loop system at high flow rates
restrictors hardly affect the pressure at all. What is STRONGLY
affected is the flow rate.
There is a about a 6 to 8 psi pressure differential
across the pump however. I'll know more next week when
I get the +/- pressure gage for the inlet side.
BTW the pump got almost too hot to touch.
Paul Lamar
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