Water pump short-cycling

[bluesofa]

I wonder if anyone has experience of this particular pump they can offer advice on?

It’s an Hitachi water pump, the model is WM-P150GX2. It pumps water from two ground level storage tanks to all the outlets in the house.

 

The pump has run well for perhaps five years now, but recently is has begun to short-cycle, i.e. when a tap is opened, the pump tends to start, stop, start stop, about every second while the tap is half-opened.

 

In the past the pump would pressurise the house pipework and just cut in perhaps every five or ten(?) seconds.

If I open the tap fully, the pump runs continuously, but it’s when there’s a lower flow-rate the short-cycling now happens.

 

Looking at the Hitachi instructions the fault-finding guide suggests the air volume in the pressure tank is reduced, telling you to remove the water out of the tank and clean the aerator. I can’t see how you’re supposed to achieve this, as it does tell you not to remove the plug on the top as the tank is filled with nitrogen.

 

It has occurred to me that perhaps it means the ‘Hopper’ needs topping up? It does show how to fill it by removing the Hopper Cap when you install the pump.

Is the ‘Hopper’ isolated from the rest of water system, or do I need to isolate the system before opening the Hopper Cap?

[Artisi]

More likely the bladder tank, either a holed diaphram or its lost gas/pressure. 

[Crossy]

33 minutes ago, Artisi said:

More likely the bladder tank, either a holed diaphram or its lost gas/pressure. 

Yup, I understand these tanks are not refillable (check if it has a car type tyre valve just in case), replacement is the fix.

[weegee]

Buy a new Bladder tank....I have the same system, and it's happened twice in 8yrs...The Bladder tank is about 1000 baht.

screw it on and everything should be normal again.

Other than that....do you have a leaky tap somewhere maybe...

[bluesofa]

1 minute ago, weegee said:

Buy a new Bladder tank....I have the same system, and it's happened twice in 8yrs...The Bladder tank is about 1000 baht.

screw it on and everything should be normal again.

Other than that....do you have a leaky tap somewhere maybe...

Thanks very much for the info. I'll have to look it that.

 

No, there's no leaky tap, otherwise I'd hear the pump cutting in regularly on its own, and it doesn't. Found a leak underground in the blue PVC pipe that way a couple of years ago.

 

No one has said that it's definitely not the Hopper /Hopper Cap? I assume it isn't but I just wanted to know for sure. Can I take the top of it just to check, without water spurting out everywhere?

[Artisi]

42 minutes ago, bluesofa said:

Thanks very much for the info. I'll have to look it that.

 

No, there's no leaky tap, otherwise I'd hear the pump cutting in regularly on its own, and it doesn't. Found a leak underground in the blue PVC pipe that way a couple of years ago.

 

No one has said that it's definitely not the Hopper /Hopper Cap? I assume it isn't but I just wanted to know for sure. Can I take the top of it just to check, without water spurting out everywhere?

if its not running there will be little pressure there. Its use is for priming the pump initially , unlikely your problem - but go ahead and look and put your mind at rest.

[Crossy]

Since this appears to be a constant-pressure type pump it could well be a stuck flow switch (this is separate from the pressure switch), marked as "life save unit" in our OP's diagram.

 

IIRC we had a poster with a similar issue a while back, taking it all apart and putting back together solved the problem although we never actually found if the switch was stuck or not. A thump with the engineer's friend (hammer) may be sufficient.

 

Otherwise take it to your local pump man.

 

EDIT I also note that both of the suggestions made in this thread appear in the fault finding guide posted by our OP

 

EDIT2 To empty water from the bladder tank unscrew it from the pump and shake the water out.

 

[weegee]

12 hours ago, bluesofa said:

Thanks very much for the info. I'll have to look it that.

 

No, there's no leaky tap, otherwise I'd hear the pump cutting in regularly on its own, and it doesn't. Found a leak underground in the blue PVC pipe that way a couple of years ago.

 

No one has said that it's definitely not the Hopper /Hopper Cap? I assume it isn't but I just wanted to know for sure. Can I take the top of it just to check, without water spurting out everywhere?

YES...Turn the power off,unscrew it (hopper cap) and make sure it's full of water. Thats a normal thing to do. I am pretty sure the bladder is the problem.

Unscrew Bladder and very gently place something in the hole to see how far it goes in and touches the actual Bladder...It should only go in a short distance to touch the bladder. If it seems to go in a long way (more than say about 20mm) the bladder is done. buy the new bladder and that should fix the problem

[bluesofa]

I’ve had a look at the Hopper. Just cracked the cap open a little and there was some water that dribbled out, so that seems OK.

 

Regarding the flow switch you said was marked as “life save unit”. I had a look there, but that has gaskets either side of it, so I’d be reluctant to take it apart. I’d imagine that trying to get five-year-old gaskets apart then back together successfully could be pretty difficult.

Unless it is mechanically linked to the pressure switch on the top of it, I don’t know how that works? There’s no cable going into the life save unit. There is however a cable the goes into the ‘pump head’ (that’s a cable separate from the motor cable). Yet again there’s gaskets involved there, so I’m still leaving that.

 

It looks like I’ll need to get someone to look at it. If I was on my own I could put up with no water while I took my time taking it apart. As there’s three of us, it needs someone who (hopefully) knows what they’re doing, to get it done quickly once started. I’ll have to ask around.

 

Thanks for all the replies, it’s very much appreciated.

[bluesofa]

On 08/02/2018 at 8:47 AM, weegee said:

{snipped}

Unscrew Bladder and very gently place something in the hole to see how far it goes in and touches the actual Bladder...It should only go in a short distance to touch the bladder. If it seems to go in a long way (more than say about 20mm) the bladder is done. buy the new bladder and that should fix the problem

 

I've been trying to find someone to replace the Bladder tank for my Hitachi pump.

First guy was convinced I needed a complete new pump, someone else had no idea about the Bladder tank.

I think I might end up doing it myself. I have found an address for an Hitachi dealer locally.

As the family are going awaya for a while, I don't have to worry about rushing it if there are any complications, although I hope not.

 

You said to unscrew the Bladder. Is it straightforward to do that by hand, or is it a very tight fit?

Before I remove it, I'd like to know what is used to seal the thread? Is it normal PTFE tape, do I need to buy something else?

Is the male thread on the base of the main unit, and the female thread inside the Bladder tank?

Is there anything else I should be aware of?

 

[weegee]

20 minutes ago, bluesofa said:

 

I've been trying to find someone to replace the Bladder tank for my Hitachi pump.

First guy was convinced I needed a complete new pump, someone else had no idea about the Bladder tank.

I think I might end up doing it myself. I have found an address for an Hitachi dealer locally.

As the family are going awaya for a while, I don't have to worry about rushing it if there are any complications, although I hope not.

 

You said to unscrew the Bladder. Is it straightforward to do that by hand, or is it a very tight fit?

Before I remove it, I'd like to know what is used to seal the thread? Is it normal PTFE tape, do I need to buy something else?

Is the male thread on the base of the main unit, and the female thread inside the Bladder tank?

Is there anything else I should be aware of?

 

Yes it's straight forward...You should be able to unscrew it with your hands, but if not large multigrips or the like will help. It's the same as changing an Oil Filter on an engine....You dont need anything to seal the thread (but thats up to you). The male thread is on the Bladder side and is Neopreen (Nylon), and the female thread is on the pump side. Turn off the water to the pump(and Power) before you start or you will get a face full of pressurised water when the bladder comes free....Screw in Bladder until nice and hand tight...Firm. When you have completed this part, then undo the cap (remove) on the actual pump and fill with water ( turn water on )...when water flows freely from the loose cap, tighten it and turn the power on. Dont panic if at first it doesnt pump, as the bladder has to pressurize as well. Open cap and fill with water again until you have complete pressure and flow. When everything is fully pressurized, the pump will stop automatically...

Hope this helps.

[bluesofa]

8 minutes ago, weegee said:

Yes it's straight forward...You should be able to unscrew it with your hands, but if not large multigrips or the like will help. It's the same as changing an Oil Filter on an engine....You dont need anything to seal the thread (but thats up to you). The male thread is on the Bladder side and is Neopreen (Nylon), and the female thread is on the pump side. Turn off the water to the pump(and Power) before you start or you will get a face full of pressurised water when the bladder comes free....Screw in Bladder until nice and hand tight...Firm. When you have completed this part, then undo the cap (remove) on the actual pump and fill with water ( turn water on )...when water flows freely from the loose cap, tighten it and turn the power on. Dont panic if at first it doesnt pump, as the bladder has to pressurize as well. Open cap and fill with water again until you have complete pressure and flow. When everything is fully pressurized, the pump will stop automatically...

Hope this helps.

Thanks weegee, yes you've explained it clearly.

 

As it seems to be a bladder problem, if I were to remove it while I'm trying to locate a new one, does this mean it wouldn't be a particular problem if I were to screw in a plastic end-plug on the pump side and continue to use it for now? 

The Bladder has been doing nothing for weeks now.  I don't know what size the pipe fitting is though?

[Daffy D]

Leave the bladder tank on the pump so you can still use it and take a photo to the shop:-

 

 

[weegee]

2 hours ago, bluesofa said:

Thanks weegee, yes you've explained it clearly.

 

As it seems to be a bladder problem, if I were to remove it while I'm trying to locate a new one, does this mean it wouldn't be a particular problem if I were to screw in a plastic end-plug on the pump side and continue to use it for now? 

The Bladder has been doing nothing for weeks now.  I don't know what size the pipe fitting is though?

As per "Daff D" said....leave it on and still use the pump as is, until you have a new one (Bladder).

[bluesofa]

Personally I'd rather take the Bladder with me, rather than a photo.

Being an untrusting guy and not knowing too much about these fittings, I wouldn't want to find there were a couple of almost identical ones, and come home with the wrong one of another model.

I can take the page with the instructions & model number on as well.

 

Thanks again for the help.

 

[bluesofa]

Update on the Bladder Tank replacement for my water pump.

 

Just received it this afternoon. I followed the instructions offered here, very straightforward. It took only fifteen minutes to replace and bleed some air out via the Hopper Cap.

Working fine now.

 

I had a price from Hitachi Bangkok of 1,712 Baht plus delivery. At the time I assumed the price of about 1,000 Baht quoted here was maybe a couple of years previously, and perhaps the price had increased since then.

 

My wife called a local Hitachi dealer, gave them all the details, including the part number. They said they would have to order it from Bangkok as well, and we would have to pay the delivery cost from Bangkok to Udon. They promised to call back with a price, but we never heard from them. I assumed the price would be the same as I had been quoted by Bangkok.

In the absence of any local price, I ordered it from Bangkok.

 

It was only after I had ordered and paid, did I discover via another member that the part was on sale at 1,200 Baht elsewhere.

I had wrongly assumed that a genuine replacement Hitachi part would be virtually the same price locally as buying it from Bangkok. Oh well, you live and learn.

 

Thank you to everyone who took the time to reply and offered invaluable advice. Cheers.