Kinda electrical. Kinda plumbing.

I recently replaced my 1/2 HP well pump with a 1 HP well pump. Why? Because it's what was readily available at the time...

Now, when the pump kicks on, I get a loud bang . I'm thinking I can either 1.) install some type of "start-up pressure absorber" device on the water line, or 2.) install some type of electrical rheostat that eases the amperage into the pump. (# 3 - "put the right pump in" ain't happening. It's 10 degrees outside.)

Any thoughts?

When it kicks on or kicks off you get the bang?
Sounds like water hammer. Perhaps a larger pressure tank or the tank closer to the point of entry into the house would help.

Only when it kicks on.

I wouldn't think it would be water hammer. Because it only started after I replaced the pump.

Logical?

(And the pressure tank is three feet from where the line enters the house.)

Where does the noise appear to be coming from? Did you install a new check valve?

The corner of the basement where the pressure tank is located.

It's a one-time klunk every time the switch comes on.

It's still the original check-valve.

My guess is the switch. What brand pump and switch did you buy?

Your tank is the shock absorber in the system you first asked about. Do you have a bladder tank or a free air control tank. Any way you could have lost air in your tank? Are you still getting fairly long cycles between motor kicking on and off? Is the noise less on startup if you have some heavy usage of water going on like a hose coming directly off the tank. Is the noise the same?

You mentioned you were not interested in replacing it with the “right” pump because of the weather. Is the pump down in the well as a submergible? I don’t see where a larger than needed pump should be causing problems. What you basically will have is a higher flow rate. When you hooked this up was there a large size reduction between the new pump and the old pipe?

Unfortunately, the cost of a VFD controller to slowly ramp up the pump speed would be cost prohibitive especially if the pump will be changed out when warmer weather gets here.
Any loose piping anywhere that could be tightly secured to minimize the kick?

It's a FloTec. Switch is Parts2o (30-50)

Submersible. 130' down.

Tank pressure should be about right. I "topped it off" last fall after 14 years of maintenance free use. Cycle time seems to be about the same.

No additional reducer needed on replacement. 1 1/2" schedule 80 PVC

My guess is the new pump just has a higher flow rate and maybe that’s where the line goes into the tank is stepped down causing a partial restriction to the inrush water so as it’s trying to compress the air in the tank it’s now also able to water hammer some. As kok328 pointed out there is a loose pipe that’s smacking against another or something like that. The 1 ½ line coming into the tank goes into what size fitting there?

'Looks like 1" PVC going into a coupler (all pipes are iron after that) before the pressure tank.

For a 1 HP motor with 6x inrush current @ 220VAC might give you 20A current for one second or so.

If you know the length and gauge of wire from source to pump you could temporarily splice in a short length of skinny wire, AWG to TBD, to halve the current.
The trick is so minimize the noise with shorter/longer splices while still supplying adequate power to operate your pump at the 1/2 hp power level and at normal efficiency.

A better way would have a relay temporarily cut in a series resistor for a second or so during startup.

With HP = Head x GPM/3946,
at 50% efficient you would get GPM = (1 hp/130')x(3946 x 0.5) = 15 GPM

Wuzzat? said:

For a 1 HP motor with 6x inrush current @ 220VAC might give you 20A current for one second or so.

If you know the length and gauge of wire from source to pump you could temporarily splice in a short length of skinny wire, AWG to TBD, to halve the current.
The trick is so minimize the noise with shorter/longer splices while still supplying adequate power to operate your pump at the 1/2 hp power level and at normal efficiency.

A better way would have a relay temporarily cut in a series resistor for a second or so during startup.

With HP = Head x GPM/3946,
at 50% efficient you would get GPM = (1/130')x(3946 x 0.5) = 15 GPM

Click to expand...

Wait a minute, maybe I don't understand something here.
The wire size is dictated by the size of the breaker and should be big enough to handle what the motor needs. On start up the motor will draw more amps
than stated on the motor and the breaker is forgiving for a second. Motors are stupid they just take what they need, changing wire size is just asking for touble or did I miss something.

nealtw said:

Wait a minute, maybe I don't understand something here.
The wire size is dictated by the size of the breaker and should be big enough to handle what the motor needs. On start up the motor will draw more amps
than stated on the motor and the breaker is forgiving for a second. Motors are stupid they just take what they need, changing wire size is just asking for touble or did I miss something.

Click to expand...

Yes, normally motors want a 'stiff' (low impedance source resistance) to start up properly while under load like this pump.

The temporary high resistance switched in by an NTC thermistor or a relay/ resistor may be enough to stop the noise for one second without unduly shortening the life of the motor.

I guess another way would be to use a damped spring coupling between the motor output and the pump input shaft, with the coupling providing temporarily more acceleration difference between the motor shaft and pump shaft which then dwindles to nothing.

Try the easiest first to localize the problem and than pick the optimum long term fix.

This issue is in addition to the current vs time needs of the motor, going from high current to low within a few seconds, and the breaker current vs trip time taking perhaps a minute or more to trip at 2x rated current and maybe 0.16 sec to trip at 6x overload.
This is another messy interaction but can be solved graphically. Matching a breaker trip curve to a pump motor current vs time curve may not be that easy, but the two curves should track other with a slight offset at all places on the curves.

If the OP really only needs 1/2 hp, feed the 1 hp motor 0.707 x 220 v = ~156V [{156^2}/{220^2}= 0.5 ] and adjust to get the noise reduction and power necessary. Now we're were back to a VFD or PWM modulator or a step-down transformer.

I didn't have to duck as most of that just went over my head anyway.
Maybe I can ask a simpler question.
Are you saying if the chart says the motor requires a wire say 10 and I run a 12 the motor will turn slower or start slower??

By starving the motor of the amperage or voltage it needs to start and run, you are simply adding heat to the windings which is what kills motors.

I would be tempted to try teeing something like this into the line along with trying to find out if there is movement where it is and secure those pipes better. I have never used one of these maybe the pros will comment on them. They are designed to be used for rapid shutoff of flow and controlling the mass of moving water causing water hammer. I don’t see the function much different than excess incoming water needing something to slow it down.

I would not recommend a makeshift method of trying to limit inrush current to the motor. If you want to solve the problem electrically there are soft start devices on the market I’m sure I have no idea if they will work well with the type motor on a deep well pump.

http://www.cashacme.com/prod_general_plumb_waterhammer.php

http://www.bigbrandwater.com/waterhammer9.html?cmp=googleproducts&kw=waterhammer9

I just showed the 1 inch model above they have a whole range up to 2 inch.

That's an idea. (The electrical guys a few posts back just made my head spin :hide

Everyone brings something different to the party, that’s why I like open forums. I always say there should be a header / disclaimer before every post including mine saying “Follow at your own risk.”

I haven’t ever used a water hammer suppressor but in looking on line there are a whole lot of them out there. Sears even has a selection they sell, and then there are huge industrial versions and even municipal sized units. They must sell as there are a whole line with PEX fittings and even Shark Bite’s.

Like I said in an earlier post your water tank should be doing this job, but if there is a restriction from the main flow down to the tank inlet some of the flow will be stopped or rapidly slowed down and it’s just my guess that’s what’s causing the bang.

They used put in a stand pipe that would go straight up and stay full of air and absorb the hammer.