In order to properly test the pump in question, you will need a submersible pump test station consisting of the these components:
- A vessel of some sort into which you can submerse the pump. An old conventional galvanized tank with a hole cut in the top works great for this. To make it easier to get the pump in and out of the tank, mount the tank at a 45-degree angle on a cradle. Then, using two lengths of 1-1/2 inch angle iron, long enough to reach from the top to the bottom of the tank, make a guide track for the pump to slide into the tank on by spacing the rails about 3 inches apart. Weld the top end to the lower side of the opening in the tank, and weld a short piece of angle between the bottom ends to keep them together.
- An accurate flow meter that has a large enough range to measure the flow rate of the largest pump you typically will service. If you service a range of pumps (from 5 gpm residential pumps to 75 gpm "gentleman farm" ag pumps), you should consider two flow meters plumbed in parallel and valved so you can run the flow through either or both. This is because the accuracy and scale divisions of a 100 gpm flow meter are not precise enough in the lower range to be of much use.
- An accurate pressure gauge - a 4-inch liquid-filled gauge with a range high enough to measure the shut-off pressure of the pumps you will be testing. Here again, two gauges that can be isolated, one with a low range, and one with a high range may be helpful.
- A quick disconnect device, like a union or cam-and-groove coupling, to facilitate the attachment and removal of the pump from the piping system. A 6-foot length of high-pressure hose also is useful. Make sure its pressure rating is adequate.
- A power supply consisting of a motor starter for three phase pumps and/or a control box for three wire single-phase pumps. You can use your amp probe to measure the amp draw of your pump while it is running.
The illustration shows how a pump test station could be plumbed.
Here is how to test pumps using this test station:
1. Start with the valve in the closed position.
2. Turn the pump on and slowly open the valve to purge the air out of the pump.
3. Once the air has been purged, close the valve all the way and note the pressure reading. This reading should correspond to the shut off pressure on the pump curve. If it does not, there is still air in the pump or it is worn from abrasion or old age. Disassemble the pump and inspect for signs of wear.
4. Open the valve until water is flowing at approximately the flow rating of the pump and note the pressure. Also note the amp reading at this flow rate and compare these readings with values from the pump curve and motor manual. If there is a significant deviation from the book values, inspect the pump and motor to determine the problem.
5. Open the valve all the way and note the flow rate, pressure and amp readings. Do not run the pump in this condition for more than a few seconds because, with no back-pressure on the discharge side, the pump could go into an up-thrust condition, which would damage the internals if left on for very long.
6. Plot these three values on the pump curve on the pump literature or manual. If the curves line up fairly closely and the amp draw is at or below the book value, the pump is fine and can be put back in service. If the flow characteristics vary more than 5 percent, or if the amp draw exceeds the book values, disassemble and inspect the pump, replacing either the defective parts or the whole pump. You will likely find the parts you need at your local pump distributor or farm store.
A simple test station like this can be a valuable tool that will take some of the guesswork out of your troubleshooting and make you a better pump person.