Hitachi Water Pump Mystery - Why is this doing this?

[steve73]

This does seem to be a fairly non-standard arrangement...  Normally the mains supply keeps the tank refilled, and the pump starts whenever a tap is opened....  The 'bypass" from mains to pump outlet is provided for direct supply only if the pump ever fails.

 

With the house piping arranged to take its supply from either the mains (which is rarely a particularly high pressure) or the pump, then even with a healthy mains pressure it would usually be less than the pump "start" pressure switch setting.  i.e. the pump would always tend to start when the house taps were opened, and the mains supply would never take over unless the pump had failed... 

 

Your arrangement suggests that in order to prevent the pump running when there is at least some mains pressure, the pump pressure switch settings have been reduced to the point at which the pressure never falls enough to start the pump (there will always be some residual pressure from the static head from the pump to the open tap).

 

By closing and opening the valve (which appears to be on the pump outlet), a small pressure fluctuation is sufficient to cause the start switch to activate and the pump to kick in. (You could test this by "tapping" the pressure switch lightly, as this is often enough to cause it to start when it is very close.)

 

My suggestion would be to (re-)adjust  the pressure switch setting so that it starts at a higher pressure.  In this way the pump will always run when the taps are opened, and the mains will only refill the tank.

In the event that the pump fails to start, then the mains will take over (providing its pressure is high enough).  I.e. return the system to the more usual arrangement.

 

The only minor downside is that the pump will operate every time a tap is opened, but the additional electricity cost will be minimal, and you won't have to go outside to "kick-start" the pump in the middle of the night every time.  Also you will have a much higher pressure every time to all of your taps.  There should be a NRV on the mains supply where it joins the pump outlet or the pump will simply recycle the water back to the tank, and if this has been missed out (highly likely if you used a cowboy plumber) this could explain why the pressure settings have been reduced... (or also if the NRV passes slightly, eg with a bit of grit or even a little bit of PTFE tape)   If you find that the pump does keep cycling when all the taps are off then a passing NRV is the most likely cause).

 

Good luck.

[sometimewoodworker]

1 hour ago, steve73 said:

My suggestion would be to (re-)adjust  the pressure switch setting so that it starts at a higher pressure.  In this way the pump will always run when the taps are opened,

While the pressure switch could have been adjusted it should be easy to see if it has as there is often a paint seal to show that it has been moved if it’s setting has been changed I would suggest putting in a new one is better as without a pressure meter you will probably have extreme difficulties in setting it back to the correct default and the pressure switch is a cheap part, usually under 200 Baht.

 

If indeed it has been fiddled with the playing about with the settings will probably do no harm in the short term I certainly would not want to over pressure PVC long term.

[hansened]

Somewhat  related.   but not. Seeking Deep well pump serviced. My LSC lucky star pup motor died.

Been there  15 yrs  so how to know if SJ or PJ.  I have two lines running out and down  to the connectors but some Hitachi SJ have two lines out also ? Anyone know of service - repair shop in Pattaya ?

 

 

Edited February 26, 2020 by hansened
forgot to check; wish to receive replies.

[Thomas J]

bankruasteve, steve73

 

i unscrewed the yellow cap and there is plenty of water.  I also checked the filler tube and there is plenty of water.  I was going to try and adjust the pressure switch but it is not very easy to determine how to do it.  If I want the pump to come on with a higher pressure than it currently does.  How do I do that?  Thank You. 

[bankruatsteve]

Are you sure you want higher pressure for turn on?  Seems like it would be lower to me.  But, I dunno.  Maybe play with it.  Mark the where the screw is now and then turn one way a little bit, if nothing happens, turn the other way a little bit.  Repeat with longer turns until you find the sweet spot.  

[Thomas J]

1 minute ago, bankruatsteve said:

Are you sure you want higher pressure for turn on?  Seems like it would be lower to me.  But, I dunno.  Maybe play with it.  Mark the where the screw is now and then turn one way a little bit, if nothing happens, turn the other way a little bit.  Repeat with longer turns until you find the sweet spot.  

Bankruasteve,

Is this the screw that needs to be turned?  Also since the pump is not kicking on when the government water pressure is sufficient wouldn't I want it to be when the pressure is high rather than low?  Or am I thinking incorrectly.  Certainly when I close the PVC valve is that increasing or decreasing the pressure that the pressure switch is registering? PS, I saw another post on Thai Visa from a person who was experiencing exactly the same as I  am. 

[bankruatsteve]

Sorry mate, I have no idea.  On my pumps, the label says "DO NOT ADJUST" so I've never been inside.  ????  Someone who does know should be along soon.

[steve73]

Yes - that is the pressure adjustment.  Make sure you use an insulated screwdriver as it is also live..!!! (you can unplug it but it's much more difficult to get the "sweet spot").

Turn it towards the + for a higher start/stop pressure.... but not so high that it won't switch off when the pump is running but no taps are open, (you need to be sure the pump is not simply recycling back to the tank if your NRV is leaking though).

Depending how old the pump is the switch sometimes sticks, so it can be difficult to get it set just right.

 

Remember you are aiming to get the pump to run whenever a tap is opened, and rely on direct mains feed only when the pump fails.

[Thomas J]

4 minutes ago, steve73 said:

Yes - that is the pressure adjustment

Steve73 

Given that the pump does not kick on wouldn't I want it to come on at a higher pressure?  Does that mean I would turn the screw clockwise? 

[steve73]

When you close the PVC valve you are probably just introducing a small pressure fluctuation sufficient to "kick" the switch to "on", and overcoming any "stickyness".  You can test this by tapping the switch lightly (with an insulated tool)...   If it is sticking too much that it won't switch off when there are no taps open, yet won't switch on when a tap is opened, then you can try spraying it with a little light oil (eg WD40), but if that fails then it's time for a new switch (about 250-300 bt).   

[Thomas J]

Just now, steve73 said:

When you close the PVC valve you are probably just introducing a small pressure fluctuation sufficient to "kick" the switch to "on", and overcoming any "stickyness".  You can test this by tapping the switch lightly (with an insulated tool)...   If it is sticking too much that it won't switch off when there are no taps open, yet won't switch on when a tap is opened, then you can try spraying it with a little light oil (eg WD40), but if that fails then it's time for a new switch (about 250-300 bt).   

Steve73

We tried the tapping and nothing.  The switch is brand new. The pump at one time would never kick on and the "plumber" replaced the pressure switch. 

 

[steve73]

It's not totally clear from the photo which is "+" and which is "-"...  Try adjusting it both ways to make the pump start when you open a tap - best to shut off the direct mains water supply so you are sure this is not providing the pressure to stop it from starting.

[Thomas J]

4 minutes ago, Thomas J said:

When you close the PVC valve you are probably just introducing a small pressure fluctuation sufficient to "kick" the switch to "on", and overcoming any "stickyness".

Steve73,

 

There was another person on Thai Visa with the same pump and had a similar problem.  His pump would kick in if he flushed a toilet but not if he ran the shower.   This is the diagram of his system.  I 'think" mine is similar since if I unplug the pump the water from the mains still flows through the pump and to the house.  If I close the PVC shut off exiting the pump it cuts the water to the house. 

 

Edited March 1, 2020 by Thomas J

[bankruatsteve]

My thinking (which might be <deleted>) is that:  the pump is the one holding the pressure in the lines.  Opening a tap reduces that pressure.  So, if the pump isn't turning on, it seems to me you need to reduce the pressure that it takes for the pump to activate.  (?)

[steve73]

Typical switches are factory set to start & stop at around 2.8 - 3 bar...  this should provide sufficient pressure to raise the water to a height of around 30m, but if your tap is higher than this the static head of water may be too high to allow the pump to start... (I'm in a 4 story town house, and my pump wont start if I open the tap on my roof... I need to open a lower one to get it to start) 

But your plumber could have adjusted it when he fitted it. 

[transam]

2 minutes ago, Thomas J said:

Steve73,

 

There was another person on Thai Visa with the same pump and had a similar problem.  His pump would kick in if he flushed a toilet but not if he ran the shower.   This is the diagram of his system.  I 'think" mine is similar since if I unplug the pump the water from the mains still flows through the pump and to the house.  If I close the PVC shut off exiting the pump it cuts the water to the house. 

 

Yes, that is how mine is, but with more valves to isolate any part of the system if a repair is needed.

[Thomas J]

3 minutes ago, steve73 said:

It's not totally clear from the photo which is "+" and which is "-"...  Try adjusting it both ways to make the pump start when you open a tap - best to shut off the direct mains water supply so you are sure this is not providing the pressure to stop it from starting.

Steve73,

I read on "most" switches clockwise increases the pressure setting.  Assuming that is correct. Isn't that what I would want?  Shutting the mains I don't think would tell us much.  The pump does run and draw from the tanks.  It is strictly that the pump does not kick on when the mains pressure is too low not non existent. 

 

[steve73]

Your problem is when the mains pressure is to low, so you need to set the pressure switch up in this situation..  Shut off the mains water at the meter to simulate this.

[Thomas J]

14 minutes ago, steve73 said:

Your problem is when the mains pressure is to low, so you need to set the pressure switch up in this situation..  Shut off the mains water at the meter to simulate this.

Bankruasteve, 
Steve73

Well I turned counter clockwise one full turn.  We will see tonight when the mains water pressure always drops after 12:00.  Thank You everyone for your help. 

[Fruit Trader]

51 minutes ago, Thomas J said:

Bankruasteve,

Is this the screw that needs to be turned?  Also since the pump is not kicking on when the government water pressure is sufficient wouldn't I want it to be when the pressure is high rather than low?  Or am I thinking incorrectly.  Certainly when I close the PVC valve is that increasing or decreasing the pressure that the pressure switch is registering? PS, I saw another post on Thai Visa from a person who was experiencing exactly the same as I  am. 

 

The Hitachi pressure switches have a small adjuster at the top for switch differential and a large thumb wheel under for operating pressure.

The pressure switch setting is optimized around the bladder tank charge pressure (normally shown on the bladder tank) and should be adjusted and tested using a pressure gauge connected to the pump outlet.

Example :-

Switch on 16 psi

Switch off 23psi

Bladder charge 12 psi
 

[Thomas J]

2 minutes ago, Fruit Trader said:

The Hitachi pressure switches have a small adjuster at the top for switch differential and a large thumb wheel under for operating pressure.

The pressure switch setting is optimized around the bladder tank charge pressure (normally shown on the bladder tank) and should be adjusted and tested using a pressure gauge connected to the pump outlet.

Example :-

Switch on 16 psi

Switch off 23psi

Bladder charge 12 psi

Fruit Trader.  Does that mean that the screw that I turned counterclockwise does not adjust anything?  I know some pumps have two different settings.  One that adjusts the range and a second that sets the shut off.  

[Fruit Trader]

Just now, Thomas J said:

Fruit Trader.  Does that mean that the screw that I turned counterclockwise does not adjust anything?  I know some pumps have two different settings.  One that adjusts the range and a second that sets the shut off.  

The screw you adjusted is the switch balance differential and the place to tweak the gap between on/off . It is normally factory sealed with a blob of paint. Its not a good idea to adjust these switches without pressure indication.

[Thomas J]

33 minutes ago, Fruit Trader said:

The screw you adjusted is the switch balance differential and the place to tweak the gap between on/off . It is normally factory sealed with a blob of paint. Its not a good idea to adjust these switches without pressure indication.

Fruit Trader,

 

As you can see there is no blob of paint.  So if I understand you correctly it merely adjusted the differential between when the pump kicks on and off not the pressure?  So if I wish to adjust the pressure there is a thumb wheel next to the bladder?  If I adjust is clockwise increasing or decreasing the pressure that the pump will kick in on? 

[VocalNeal]

May have been stated before but there needs to be a check valve in the city water supply line . Otherwise when the pressure drops and the pump starts the pump will short circuit raising the pressure which will shut off the pump. 

The check valve will shut off the city water while the pump runs but the city water will flow again once its pressure is restored.

Why not simply shut off the city water to the pump and allow the city water to fill the underground tank and then run the house always on the pump.

[Thomas J]

2 minutes ago, VocalNeal said:

Why not simply shut off the city water to the pump and allow the city water to fill the underground tank and then run the house always on the pump.

VocalNeal

That may be the solution but I am not sure where the shut off is from the mains to the pump.  I have to do some investigating. There are two shut off valves at the street.  Perhaps one is to the pump and the second to the tanks. 

 It would appear as though whoever put in this system originally ran PVC from the mains directly to the pump and a second run of PVC to refill the tanks.  

[bankruatsteve]

For me I prefer to have the city mains provide water when it can. Why run a pump if not necessary? But I have two manual Valves to set, one on the other off to change over. Even my wife knows how to do. 

Edited March 1, 2020 by bankruatsteve