water pump, pressure accumulator

[h90]

My water pump (Hitachi, not old but no warranty because previously the ant lived in the pressure switch and I had to take it apart).

Now it starts to rapidly turn on/off if there is a water demand. Means that water pressure accumulator (or however the correct name is), is either broken or out of pressure.

I know it only from oil hydraulics. There it is basically a rubber bag or rubber closed area which is filled with compressed N2.

So I assume that it is the same with a water pump.

Is it possible to check if it is broken or just empty?

Is it possible to refill it or do I need a new pump?

Thanks

[h90]

no one ever repaired a normal water pump?

[Crossy]

Your assertion is correct, it's almost certain that the accumulator is waterlogged.

Not all tanks have a bladder, if yours does and it's failed, time for a new tank

With a non-bladder tank it may be as simple as turning off the the water and power, opening the valves at top and bottom of the tank, letting the water run out and re-closing everything.

With a bladder tank there's usually a car-tyre type valve which you can use to re-pressurise the bladder, it will be easiest to release all the water pressure (like for the non-bladder tank) before pumping up to the recommended pressure (label on the tank hopefully).

[h90]

Your assertion is correct, it's almost certain that the accumulator is waterlogged.

Not all tanks have a bladder, if yours does and it's failed, time for a new tank

With a non-bladder tank it may be as simple as turning off the the water and power, opening the valves at top and bottom of the tank, letting the water run out and re-closing everything.

With a bladder tank there's usually a car-tyre type valve which you can use to re-pressurise the bladder, it will be easiest to release all the water pressure (like for the non-bladder tank) before pumping up to the recommended pressure (label on the tank hopefully).

new tank means new pump, or? I guess I can't buy only the tank, or, as it is one specific set?

[Crossy]

new tank means new pump, or? I guess I can't buy only the tank, or, as it is one specific set?

Most parts for the common pumps are available as spares, your local pump-shop should be able to advise and obtain. Whether it's financially viable is another animal altogether, a new pump may end up cheaper.

Task A is to determine if the tanks has a bladder and if it's ruptured, it's possible that the air has simply left via a leaky valve.

[HooHaa]

there is an adjust screw that will allow you modulate how often it turns on or off to keep the pressure up.

There is a cylindrical pressure switch with a plastic cap, usually grey.

take off the cap and turn the screw marked + and - until the motor stops kicking in so frequently.

oh and i have replaced the pressure bell on my mitsubishi, its not that expensive

Edited January 24, 2014 by HooHaa

[h90]

there is an adjust screw that will allow you modulate how often it turns on or off to keep the pressure up.

There is a cylindrical pressure switch with a plastic cap, usually grey.

take off the cap and turn the screw marked + and - until the motor stops kicking in so frequently.

oh and i have replaced the pressure bell on my mitsubishi, its not that expensive

yes I took this apart half a year ago, and it might de-adjust itself. If you turn on the water just minimal you have pump switch twice a second with noticeable pressure change in the water flow.

So I am pretty sure it is not the screw, as the water pressure reacts too fast....I still might be wrong but I think it is pressure accumulator.

[h90]

new tank means new pump, or? I guess I can't buy only the tank, or, as it is one specific set?

Most parts for the common pumps are available as spares, your local pump-shop should be able to advise and obtain. Whether it's financially viable is another animal altogether, a new pump may end up cheaper.

Task A is to determine if the tanks has a bladder and if it's ruptured, it's possible that the air has simply left via a leaky valve.

Thanks! I didn't know that there are spares....

[jackflash]

Switch off the pump and let some water out, then check the air pressure in the accumulator.

(recommended pressure probably written on tank, else see users manual).

If the pressure is down, pump it up again and see if it holds

If it continually goes "flat" the internal bladder is broken and the whole reservoir will need replacing.

[wayned]

Switch off the pump and let some water out, then check the air pressure in the accumulator.

(recommended pressure probably written on tank, else see users manual).

If the pressure is down, pump it up again and see if it holds

If it continually goes "flat" the internal bladder is broken and the whole reservoir will need replacing.

If it has a valve to add pressure, a tire valve, if the bladder is broken, water will come out of the valve when you depress it, not air. I have 3 Mitsubishi pumps and they do not have bladders. If they become water logged you have to drain them as Crossy said and that will usually fix the problem. I also use an irrigation pump for drinking water that has a small accumulator tank with a valve. I occasionally pressurize it to 8psi, bicycle pump not Nitrogen, and the on/off slows down.

Parts are available for the Mitsubishi pumps as I have repaired them in the past. A new tank for the WP155 was 1200 baht and a top cover for the pump was 675 baht. I've also repaired a neighbors Japanese pump twice, ITC I think, which is a bladder pump. New tank was about 1000 baht. I have not seen a Hitachi but from reading their website I think that they are non bladder also.

My 2 baht worth!

[h90]

Switch off the pump and let some water out, then check the air pressure in the accumulator.

(recommended pressure probably written on tank, else see users manual).

If the pressure is down, pump it up again and see if it holds

If it continually goes "flat" the internal bladder is broken and the whole reservoir will need replacing.

If it has a valve to add pressure, a tire valve, if the bladder is broken, water will come out of the valve when you depress it, not air. I have 3 Mitsubishi pumps and they do not have bladders. If they become water logged you have to drain them as Crossy said and that will usually fix the problem. I also use an irrigation pump for drinking water that has a small accumulator tank with a valve. I occasionally pressurize it to 8psi, bicycle pump not Nitrogen, and the on/off slows down.

Parts are available for the Mitsubishi pumps as I have repaired them in the past. A new tank for the WP155 was 1200 baht and a top cover for the pump was 675 baht. I've also repaired a neighbors Japanese pump twice, ITC I think, which is a bladder pump. New tank was about 1000 baht. I have not seen a Hitachi but from reading their website I think that they are non bladder also.

My 2 baht worth!

Nitrogen is used in hydraulics, as way higher pressure (150-300) bar, with oil Oxygen in the air could cause a combustion like in a Diesel engine.

But of course at a 2 bar water pump normal air will do....

(I just tried to apply my knowledge, recently gained on a broken hydraulic accumulator on the water pump).

[h90]

Update:

I cut the electric to the pump.

could not find any valve for air.

opened a screw close to the bottom.

Opened a screw on top of it.

let the water out.

Closed the screws and opened the water, turned on the electric and everything is OK.

Pressure switch is not working perfect, in my opinion the pressure difference between on and off is too small, but sometimes it almost does not switch off.

(Before I had the ants inside and let it stuck a bit so the contacts are burned and cleaned, taken apart and fit together, bent in shape per feeling, now it switched on/off ever second or half second for I don't know how many days.).

THANKS for the help, everyone!!!

Edited January 24, 2014 by h90

[Crossy]

Great news.

I'd be spending a few Baht on a new pressure switch rather than messing about with the old one if it's got bent and burnt contacts. We've had ants in ours, even after cleaning they're never quite the same again.

You could get a more expensive switch with adjustable start and stop points, talk to your pump shop.

[h90]

Great news.

I'd be spending a few Baht on a new pressure switch rather than messing about with the old one if it's got bent and burnt contacts. We've had ants in ours, even after cleaning they're never quite the same again.

You could get a more expensive switch with adjustable start and stop points, talk to your pump shop.

yes this one is in bad conditions....this one is adjustable, but when you look at that all in plastic construction you know that you better don't change anything. Alone by screwing in or loosing the screws the head almost brakes....special quality steel.

I'll check it out...new switch would be a good idea......saves electric as well.

[JoePai]

Switch off the pump and let some water out, then check the air pressure in the accumulator.

(recommended pressure probably written on tank, else see users manual).

If the pressure is down, pump it up again and see if it holds

If it continually goes "flat" the internal bladder is broken and the whole reservoir will need replacing.

What should the air pressure be in the bladder ?

[Crossy]

Switch off the pump and let some water out, then check the air pressure in the accumulator.

(recommended pressure probably written on tank, else see users manual).

If the pressure is down, pump it up again and see if it holds

If it continually goes "flat" the internal bladder is broken and the whole reservoir will need replacing.

What should the air pressure be in the bladder ?

It should say on the tank.

Our baby LuckyPro says 200kPa (30 psi). You should be able to achieve that with a hand/foot pump.

[JoePai]

Many thanks for that - I was getting worried as the pressure the dealer told me was far higher and I was sure that was not correct

Cheers

[h90]

Update...if it helps someone else:

The problem came again after 1 week and than again.

Reason: Somewhere on the top of the tank air leaks out slowly.

I tighten all screws and pressure switch. I think it is where the pressure switch is mounted. Unfortunately all is plastic so you can't tighten strong.

After tighten it is now either OK, or the problem comes at least much slower.

[Crossy]

Soapy water may help you locate an air leak, remember fixing your bike when you were young?

If it is seeping around the threads of the pressure switch, a couple of turns of the PTFE plumbing tape will help it seal.

[Pib]

h90,

What kind of water pump are you talking about exactly. One that has a motor/manifold assembly setting on top of the pressure tank of around 15-20 liters in size or one that has a screw-on pressure "bottle" around 2 liters in size?

[h90]

Soapy water may help you locate an air leak, remember fixing your bike when you were young?

If it is seeping around the threads of the pressure switch, a couple of turns of the PTFE plumbing tape will help it seal.

Good idea......

[h90]

h90,

What kind of water pump are you talking about exactly. One that has a motor/manifold assembly setting on top of the pressure tank of around 15-20 liters in size or one that has a screw-on pressure "bottle" around 2 liters in size?

The first one. The motor and everything else is screwed on top of a pressure tank of roughly 15-20 liter.

[JAS21]

Go here and see if you can find your pump. http://www.hitachi-th.com/hitachi_new/products/index.php?lang=&menu=11 Then download the user manual and see if it helps.

If yours has the blue tank underneath the pump then there shouldn't be any water in that tank. Drain it out again, if it fills up again then you have a little problem.

[Pib]

h90,

I'm going to assume you have a pump which looks kinda like below but I'm not 100% based on your description...posting a picture along with identifying the model number off the pump's identification plate would clear all of this up. I see so many pump threads that go on and on and everyone seems to be giving advice on a certain pump type then the OP says, Oh, but my pump not like that, it's a XYZ pump...here's a picture.

Anyway, "if" you Hitachi pump looks kinda like below image here are some of my thoughts:

Your problem description so far does indicate your pressure tank is waterlogged (i.e., lost its compressed air cushion/energy spring). If the tank was transparent to where you could see inside a properly operating pressure tank, you would see approx two-thirds of the tank (bottom portion) filled with water and the top 1/3 empty since it only composed of compressed air. That compressed air is basically a compressed air spring which forces water out when water is being drawn...give gives the pump motor a rest. The spring presses down on the water, forces it to your house, until the pressure in the tank drops to the pump's lower pressure limit which would cause the pump to turn on, suck in water, replenish water in the tank, continue to push water out to the houses if the water is still be drawn and once the pressure is built back up to the pump's upper limit it cuts off....and during the pump-on portion of the cycle the water being sucked into the tank to refill it also recompressed the air recharging the air energy spring. Now the compressed air spring provides the energy to continue to push water out of the pump to the house giving your pump motor a breather. Then this cycle repeats itself over and over. If you have a small leak somewhere, the air energy spring keeps pushing the water out until the pressure drops to the pump's lower pressure limit and turns the pump on. With no air energy spring "and since fluid can not be compressed to store energy" the pump motor basically must stays on/cycling really quick even for a very small request of water...even for a leak.

The type of pump shown in the image and common in Thailand (I have a Mitsubishi model) "does not" use a rubber bladder to keep the air and water separated. So, since air is "naturally & slowly" absorbed into water the air energy spring in your tank will slowly be absorbed into the water which means your air energy spring disappears "unless slowly replenished at the same rate it is slowly absorbed into the water." It's going to vary from pump to pump, but the air could be totally absorbed with a few days to say a max of two weeks if the air is not being slowly replenished.

I expect you have already tried killing power to the pump, cutting off the pump's water inlet and outlets, removing the drain plug at the bottom of the pressure tank, letting the water "completely" drain out so air can rush into the tank so it can be compressed (air can't get in until the water is completely drained", turn the inlet/outlets and power back on, and give the pump about 30 seconds to refill itself and charge back up to pressure. During this process the air energy spring was recreated at the correct amount. You check the operation of the pump and it now operating normally again...doesn't cycle on and off way too much, even when water is not being drawn anywhere. However, but, over the coming days you being to notice the pump is beginning to cycle more...run longer than it should...and after a week or two it back to cycling on and off all the time...maybe the pump is now overheating....driving you crazy and maybe the neighbors also.

Well, what has happened here is the air in the tank probably didn't leak out as a external leak which could be found with soapy water or seeing water coming out after all the air has already leaked out. Instead, the air in the tank was naturally and slowly absorbed into the water because remember there is no barrier between (like a rubber bladder) between the water and air in the pump's pressure tank for this kind of design. Your air energy spring is now gone.

Now, remember I talked about "slow replenishment" of the air energy spring." What could very well be your problem, is the pump's air charger/control valve is defective because they are nothing more than a rubber diaphragm with a few check valves which operate buy sucking in a little out from the outside environment and injecting that little bit of air into your pressure tank/incoming water stream each time the pump cycles on and off. This keeps the air energy charge in your pressure tank replenished. Take a look at above image and in the top right hand corner you see a square looking valve with a small black PVC hose feeding back into the water inlet side of your pump....that is your air charge/control valve. What usually goes bad with these valves is the rubber diaphragm inside ruptures (and a ruptures may just be pin-hole size) from age, hard water deposits, constant back and forth movement, etc.

If you pump works normally after completely draining and refill the pressure tank like described above and works fine for a few days but then start to go down hill again, you probably have a defective air charger valve. New ones cost around 500 to 800 baht. When replacing the valve be sure to completely drain the water in the tank to get the correct initial air charge back and then the air control valve will take over and keep it at the proper level assuming you don't have any leaks in the top of the tank/manifold assembly somewhere...if you had such leaks they should be easy to spot.

Pib

P.S. Don't mess with the electrical pressure switch unless you know exactly what you are doing and have a water pressure gauge to ensure the upper and lower pressure limits are properly set....miss set pressure limits can damage your switch/pump motor.

[divylamba]

I think it will not be repaired so you have buy new water pump.You can buy any other water pump.I bought a water pump from donex last month.It is made of good quality and working properly.

[Chilon]

Hi,

On a related topic I have an Hitachi pump that stopped working due to ants in the pressure switch. After cleaning the ants out the switch initially functions OK as the taps are turned on then off. However after an hour or two the pump comes when a tap is turned on but then stays on.

I'm planning on buying a new pressure switch but the local Global in Kamphaeng Phet doesn't stock them so I thought I might see if I can adjust the settings( the cover does say don't adjust anything so I assume there is risk involved but.... )

I'm guessing there should be 2 adjustments-one for the lower pressure limit and one for the upper but I can only see one screw on the top that could have anything to do with an adjustment.

Any suggestions or does anyone know of a store around Kamphaeng Phet or Nakhon Sawan that could stock a replacement pressure switch?

[Crossy]

The simple pressure switches have only a single adjustment, for cut-out pressure, the cut-in pressure is a (relatively) fixed pressure below the set cut-out.

You can adjust them, carefully. With the lid off the switch and the pump running, carefully turn the adjustment to the low end (there are live parts in the switch, take care), the pump should cut out at some point, give the adjustment a further 1/4 turn. Test that the pump goes on and off as expected.

It's possible that the pump isn't developing its rated pressure due to a blockage or damaged impeller, so if you have to turn the switch a long way it could be time for a new pump (or a service).

[Chilon]

Crossy,

Thanks-that makes sense regarding the pressure limits. I did try some small adjustments( with power off )on the screw( both ways) without any obvious effect once I switched the power back on. It was difficult to know which way to turn it since there were no +/- markings on it.

As you say it could be some other problem or I may have caused some damage when the switch was de-anted

I'll take up your suggestion and try again with the power on and the pump active.

Appreciate the advice.

[Crossy]

The adjuster on our (cheapo) LuckyPro pump changes the pressure on a compression spring.

Reducing the spring tension reduces the cut off pressure, you can easily see the spring plate moving when you turn the adjuster so it's possible to determine which way is up.

EDIT I didn't say it, but when you need to do your adjustment when the pump is running with all the taps closed of course.

[T_Dog]

We have this same plastic Hitachi pump and it was very problematic initially. The 4 Star or Lucky Pro pressure switches are much better than the original as the replacements have 4 times the contact area. (Our Hitachi switch was also overcome by ants.) Also, there is a hose connecting a diagphram to the air injecter that has compression fittings that are very difficult to seal. As the OP mentioned, the plastic construction of the pump makes maintenance tougher as you have to be very careful to not over-torque things as you put it back together. I normally like Hitachi products, but this pump model is not very rugged.