Question
QUESTION: I have an HSJ20 (2 hp, 220V) in operation for 6 years successfully that draws from a shallow lake for our home use and irrigation.  This morning, after the sprinklers had run during the night, we had 0 pressure.  The pump motor had power but was not running during the last sprinkler cycle...instead all the water from the pressure tank had drained into the yard via the sprinklers.  The pump motor housing was extremely warm.  I turned off power to the pump for about 2 hours and when I turned back it on all was fine.  I checked for air leaks in the intake and found none.  I also checked the intake for debris/clogging and found none.  This evening I ran the sprinklers for about 40 min as a test and checked the pump motor housing and it was extremely hot. This has not been the case for the past 6 years, so something is different.  For tonight I turned off the sprinkler system but this isn't a long term solution.  Please help & thanks!

ANSWER: Good question.
It appears as if the pump motor is drawing to much current (amps) and overheating. Most motors have a thermal shut down switch which prevents them from burning up. The extreme heat of the motor is a good indication the thermal shut off worked and turned off the pump last night. Why?
If the pump was trying to pump too much water this could cause it. A zone valve not shutting off while the next valve came on could do this. Or, the bad news, the motor may be going bad. You will need to check the amp draw of the motor and compare it to the "nameplate" amp draw. It's the tag on the motor and there will be a "maximum amps" number.
If the amps on each zone are under the max. then I would suspect a problem with one of the zones not shutting off properly. If the amps just keep going up the longer you run the pump, then I would suspect the motor is going bad.
Reply back if you need more directions or help.

Matt


---------- FOLLOW-UP ----------

QUESTION: A couple of questions:
1. Is it wise to replace the motor only, or should I buy a whole new assembly of motor + pump?
2. Please elaborate on your statement regarding the pump trying to pump "too much" water.  My understanding is that the pump can only pump up to X gallons per minute.  If multiple zones were on, the pressure & volume of water would be low but the pump should still pump the same amount.  I don't understand how less pressure on the output side of the pump would cause a higher amp draw.

Answer
Good to hear from you.
1. With shop labor rates so high, it may costs as much to replace the motor as replacing the whole pump. I can do the work myself so it's not a costly item for me.
2. All centrifugal pumps have an "efficiency range" which they are designed to operate. X pressure at Y gallons per minute. When the pressure goes up the flow goes down, the opposite is also true when the flow goes up the pressure goes down. It's referred to as a "pump curve". The intention of pump selection is to have you system operate in the middle, which is the most efficient. Your pump has a range of 1GPM to 60GPM with 28-33GPM as the efficient range.
3. To move water requires energy. The more water you use the more energy. Your supplying the pump with volts and amps. Volts X amps = watts, which is a measure of energy. The volts can't go up, you only have available 120 or 240 volts, so when the pump needs more "energy" to pump more water it draws amps. Once you get to a point where the motor is drawing more amps than it is designed for it gets hot. Click, off goes the thermal overload.
In a less technical explanation, if you carry 10lbs up a flight of stairs you require so much energy to preform this task. Now, if you have to carry 100lbs up those same stairs, it requires much more energy. You are still doing it with the same body, just not a well. You get hotter and hotter until your overload pops.
I hope this is understandable, it is difficult to condense all pump operations in such a forum.

Matt