Vibration and noise from water pump inlet

[wunof11]

Here’s the short story. http://www.plumbingforums.com/forum/images/smilies/smile.gifI have a 1.5 hp Nocchi jet pump on top of a 20 gallon galvanized iron pressure tank (no bladder or diaphragm). Pressure switch is set to cut in at 20psi and cut out at 40 psi. The set up has been working well for a couple of years until a couple of weeks a ago, for no apparent reason, the inlet piping vibrates and hums/thrums as the tank pressure drops. The vibrating and humming stops when the pump cuts in to fill the tank. Some details I noticed in the most recent observations, the tank will pressure up to 40psi and cuts out as set but steadily drops to about 35 psi and holds. When the taps or showers are in use the pressure will drop and as it reaches 30 psi the humming/thrumming/vibrating starts until the pressure reaches the cut in setting of 20 psi and the pump kicks in to fill the tank.

The pump is supplied from a 150gal reservoir to pump water up to two stories, and the reservoir is filled constantly and no blockages observed.
I’ve drained out the tank from the bottom drain plug and refilled with water to no avail. I’ve tried resetting the pressure switch cut/in/out setting down to no avail. There’ really been no impact to the in house water supply but I am sure I am doing the pump damage with the vibrating and humming.

On a side note, the piping from the reservoir is all pvc with 4 90 degree joints before finally connecting to the pump inlet. These joints are a constant source of leaks and I want to swap them for a single clamped on 1 inch flexible hose form the reservoir to the pump inlet. Is there any reason not to go this route? I did see somewhere on the internet that the flexible hosing as well as too many angles in getting to the pump inlet is not recommended, although no explanation was given.

Thanks for your help...

 

[speedbump]

I'm surprised you've gotten two years out of that pump.

Elbows are friction and friction slows down water flow. If you can put poly in place of the pvc without kinking it, you would be better off. Having air leaks in the suction line isn't good either.

The noise is puzzling. Maybe a check valve leaking back slowly making a whistling noise.

 

[wunof11]

It's more than whistling though, it's vibrating and the humming/thrumming is quite loud, I can hear it from the second floor. If it is a check valve, is that usually repairable or should I call it a day on this pump. Lastly, your note that perhaps this set up should not have lasted 2 years, is it the pump brand you were commenting on or the general set up with the angles and stuff.

 

[wunof11]

So here's an update I went ahead and swapped the fixed PVC piping with flexible hoses and the noise and vibration is gone. Didn't expect that would be the solution to the noise but we wont look a gift horse...

 

[speedbump]

Glad you got it to stop.

The comment on the two years was on the pump. Those things are about as cheap as you can get.

 

[wunof11]

Great, when it finally goes I'll know enough to avoid the brand. Thanks.