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  1. #1
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    Constant pressure or accumulator type pumps

    I am going to install a water tank and pump system at my house. I have had a good search around and seen endless threads but I couldn't be arsed looking any further and hope the title will give a definitive answer for future peoples searches.

    What type of pump do I need? The small box shaped (constant pressure) Or the ones with a tank underneath (accumulator)?

    I was going to go with an accumulator type as I had a bad experience in a rented house with a constant pressure type one cycling like mad whenever a tap was opened slightly and was forever out there at all hours fiddling with the pressure switch settings. Also these come on even if you just want a glass of water etc, small amounts.

    The accumulator type will supply an (accumulated) head of pressure so it won't come on every time you crack open a tap, it will deliver pressure until it gets low then start so it shouldn't need to run as much saving electricity (electric pump start currents are 7 times the running current)

    My big question is do the accumulator types supply a constant pressure like their smaller box shaped brethren do? Any chance of when taking a shower for example it will cycle and deliver varying pressures of water? My thinking is no, once a tap is running the pump will run and only cycle at small openings (and even then at a much less rate than the constant pressure type.)

    Any experiences, pro's or cons on these two different types of pump?

    Oh, also I want to future proof it and buy a bigger pump than I need right now. I have 2 bathrooms, kitchen and front and back garden hoses (single sory) that must be able to run together. I may add another bathroom (which may be on a second story) and reticulation later so need to account for that. I was thinking of a 300w pump. Is that overkill? Right now it is a good price, only 400B dearer than the 250w one.
    Fahn Cahn's

  2. #2
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    we have an Hitachii Wm330 GX series on-demand type pump, I think you called them constant pressure although it seems to be sitting on a small tank to equalise the pressure

    works well, does not recirculate like mad, comes on when needed, feeds our 3 storey house of several bathrooms, hoses and kitchen etc

    you should not try to adjust the pressure settings on these pumps, that can lead to problems
    I have reported your post

  3. #3
    Have you got any cheese Thetyim's Avatar
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    Quote Originally Posted by Bung
    I was thinking of a 300w pump. Is that overkill?
    No, that will be fine.
    The pump recycling time depends on the flow rate and the size of the buffer tank.
    You can always add an extra buffer tank.

    I expect the shower will drop delivery if you have a garden hose on though

  4. #4
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    I think I will go with the accumulator (buffer type with a tank below it). They are a bit more expensive but don't need to turn on if you just want to fill a glass of water etc. Best bet would be an inverter type but then you are talking some $$

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    "Constant pressure" type pump (5HP), only way to go more volume & PSI for less bucks! need to have a pressure tank though with the pressure switch hooked up to it. You will be able to run 2 showers and a water hose with no loss of Psi.....

  6. #6
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    Which is what I plan to get? A pump with a pressure (accumulator tank)under neath, built in. I think you are talking about a normal pump and buy a separate pressure tank. I had one to water my farm and it was great, 3/4 inch pipes and it flowed a lot but way too much for my little baan. Actually if the place wasn't so far away I would go and grab it before someone else does, no one is living there any more.....

  7. #7
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    I have this setup, since we have a 3 floor house and the water pressure system is on floor level.

    1. Incoming pipe goes to 2500 liter tank, incoming closes with a balancer that goes up,similar to what is found in a toilet tank

    2. Water pump

    3. Flow control, will switch off pump if no water coming to pump ( that device was found installed before pump earlier, moved it after pump where it belongs following instructions and seen we had no water some times...)

    4. Tank 1000 liter

    5. Pressure switch on upper part of pressurized tank, set at 6 bars. Goes with a connection to the flow control.


    The showers that are on second and 3rd floor have normally steady flow. But since all is on single line 3/4 pipe, if someone takes shower on each floor same time, there is less flow here and there...

    A problem we have is the 1000 liter stainless tank, that is of thicker stainless gets a hole and there is leaking water jet, we had to weld close 2 places in last year, the tank is 5 years old. If you not notice then pump is on and off, hmm bit more then usual.

    If a leak occurs on a not well closing tap or in the pipe system lots of water gets discharged, requires proper build with good materials, not the case in the house we have actually, so each month a problem here or there...

    Water piping and toilet tank system are of higher end but crap so, we had other problem with toilet bowls, the balancing switch does not close properly and water is constantly supplied to overflow of toilet tank, it gave us once 5x consumption in one month, a bill of 2500 compared to 500 normally.

    If i have to build a house i would probably see for a tank that is placed on top or above house level, still requires the water to be pumped up, but prolly better then pressurized big tank we have actually.

  8. #8
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    ^ English is not your first language I presume

    but your set-up sounds like it needs a good overhaul

  9. #9
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    Quote Originally Posted by forreachingme
    A problem we have is the 1000 liter stainless tank, that is of thicker stainless gets a hole and there is leaking water jet, we had to weld close 2 places in last year, the tank is 5 years old. If you not notice then pump is on and off, hmm bit more then usual.
    This has surprised me as I was going to get a SS tank...I guess they just use poor quality chinese SS but I would be pissed having to patch one after 5 years....Looks like the plastic (?) ones will be the way to go? The newer ones do look a little better and have all the "nano" and "anti bacterial" bollocks.

    Something to research today....

  10. #10
    Have you got any cheese Thetyim's Avatar
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    Nah, get a SS tank but get a quality one.
    Ours is nearly 10 years old and looks as new.
    On the same water tower we have 2 x 1000litre plastic tanks that are a pain in the arse and a huge water filter which has corroded badly.

    The plastic tanks collect sediment in the bottom and are hard to clean, the SS tank has a bell bottom and cleaning out the sediment involves turning a tap on.

  11. #11
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    I have a water pump that comes on every 30 minutes or so for just a second. I've checked for leaks several times and nothing is leaking. Any advice or comments would be greatly appreciated.
    Also, is it possible the pump could be loosing it's prime?

  12. #12
    Have you got any cheese Thetyim's Avatar
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    It is losing pressure somewhere.
    Check the one way valve on the inlet side.

    Once every 30 minutes is not excessive.
    I would ignore it.

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    I found that the check valves were a pain in the arse getting small things trapped in it an leaking back (you need a check valve in the system so it hold pressure in the line) I think the all in one pumps have them built in. I was told to buy Hitachi over Mitsubishi as it has a bronze check vale as opposed to a plastic one in the mitsu.

    I looked at the Hitachi 300w ones but they have a bigger inlet/outlet (1,1/4"?) compared to the 250 which seemed to match my pipe size better so I think a 250 would be plenty? Home pro have signs on all the pumps now saying how many taps they can run which is great as they must get tired of explaining it x times a day. the 300 says 5-6 taps and the 200 says 5. 5 would be plenty for my needs. I live alone at the moment. The inlet /outlet sizes of the 250 are the same from the 100,150,200,250 series so 250 being the most powerful of that range. Once you go to the 300 it is the series of biggest pumps, way more than what I need.

  14. #14
    Have you got any cheese Thetyim's Avatar
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    Quote Originally Posted by Bung
    I think the all in one pumps have them built in.
    Yes they do.
    The cheap external ones are crap and only last about 2 years

  15. #15
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    Thanks guys for the tips.

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    Quote Originally Posted by Bung
    I looked at the Hitachi 300w ones but they have a bigger inlet/outlet (1,1/4"?) compared to the 250 which seemed to match my pipe size better so I think a 250 would be plenty?
    don't choose your pump on existing pipe size, you can easily put an reducer in line to match pipes

    prob 250 would be enough for you, as long as you don't want to add new bathrooms etc in the future

  17. #17
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    Ok, that is interesting as I may add another bathroom later on a second story but really, I guess it is all about how many people are living in the house and how many taps/showers are on at once.

    For me living alone it will be a shower and possibly 2 outside taps for sprinklers/reticulation at most. My son stays but he only showers while I have to watch and give commands on how to do it properly. There may be erm, house guest staying as well as the very occasionally friends visiting.

    As i mentioned before, the 300 is on special at Global, only 4oo B dearer than the 250 so that may be the go.

    Am I right in thinking that a bigger pump will deliver the same pressure and volume to 1 tap as the smaller one but can handle more taps/showers without a reduction in pressure or volume? ie, if only using 1 tap will the bigger pump cycle given its ability to deliver more pressure (higher wattage motor) and volume (bigger inlet/outlet)? Where as the smaller one would just run continuously on one tap? I wouldn't like to have a bigger pump that just cycles on 1 tap better to have it run continuously.

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    depends on the model...they have different pressures and volumes

    some pumps are made to deliver water up several stories so need a greater pressure capability, some are made for delivering water to many outlets so have a greater volume capability

    just get a pump that is suitable; both the 250 and 300 sound fine

  19. #19
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    Quote Originally Posted by ralphlsasser View Post
    I have a water pump that comes on every 30 minutes or so for just a second. I've checked for leaks several times and nothing is leaking. Any advice or comments would be greatly appreciated.
    Also, is it possible the pump could be loosing it's prime?
    I've found with an accumulated type pump, a slightly dripping tap can be enough to cycle the pump ever 30-180 minutes or so.

    One thing to bear in join with accumulated type pumps is in the majority of cases there is no membrane between the air and water in the tank. this means that over time the air dissolves into the water and the accumulator becomes less effective as reducing pump cycling for small water flows. its worth once a year or so, isolating the pump and draining the accumulator tank.

    If I were to buy a new pump I would probably look into the benefits of using a constant pressure pump with an inverter. has anyone had any experience with these? are they worth the extra money?

  20. #20
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    I was told to buy Hitachi over Mitsubishi as it has a bronze check vale as opposed to a plastic one in the mitsu.
    I was at a house recently where they didn't have a tank type pump and it sounded like an anti-aircraft gun when the lady of the house was washing vegetables. That being said theirs was a bungalow and that makes a difference because the tank type holds the head so water is instantaneous on the upper floors.

    The spring is more important than the valve material. We have Mitsubishi can't remember what the spring is but what I would do is buy the pump from a "pump" shop and ask if they have a spare check valve. If so buy that model.

    Our office is rented. I noticed after a couple of years that the pump had water hammer when it stopped, probably had it all along but..., on investigation I found the spring was missing and the valve had been fixed by a handyman, with a stone to weigh it down. TIT

    Armed with photo of the pump I went to a shop where I have seen pumps. New valve 75 Baht c/w spring, now it is quiet.

    If the pump is too big it will cycle more often. I think what one needs is enough to have a shower when someone else flushed a toilet. Unless you have teenage daughters/MIL etc. and two showers.

    Two pumps and a storage tank only if you have a history of water shortage or run a bar.
    Last edited by VocalNeal; 18-11-2011 at 02:53 PM.
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  21. #21
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    Quote Originally Posted by VocalNeal
    I was at a house recently where they didn't have a tank type pump and it sounded like an anti-aircraft gun when the lady of the house was washing vegetables. That being said theirs was a bungalow and that makes a difference because the tank type holds the head so water is instantaneous on the upper floors.
    I had the same in a rented house. I found that the air had escaped from the little acculuator tank so it had no "buffer" When they opened up a tap a little it would go mad cycling on and off. The trouble with Thais is they will just let it carry on like that as if it is perfectly normal. Obviously running it like that will shorten it's life dramatically. It is fine if you are around but if you go away and leave it up to them....Well, it will carry on until it dies then there will be a phone call asking for money to fix it.

    Quote Originally Posted by VocalNeal
    Two pumps and a storage tank only if you have a history of water shortage or run a bar
    Just to be clear, you can run a pump without a tank but you will be sucking all the pressure away from your neighbours, you will suck up any crap in the pipes (bits of plastic, thread tape, mud etc from when they work on the pipework up stream) straight into your pump, it is illegal and is just wrong. You need a tank to hold a spare volume of water if the supply cuts off altogether and it will settle out any bit's of crap to the bottom of the tank where it can be drained off.

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    Just to be clear, you can run a pump without a tank but you will be sucking all the pressure away from your neighbours, you will suck up any crap in the pipes (bits of plastic, thread tape, mud etc from when they work on the pipework up stream) straight into your pump, it is illegal and is just wrong. You need a tank to hold a spare volume of water if the supply cuts off altogether and it will settle out any bit's of crap to the bottom of the tank where it can be drained off.
    You need to check the water pressure where you are. Where I am in Bangkok it barely dribbles at waist high say 1m pressure so in the tank scenario you would still need a pump to "suck" the water.
    If you are building new then a tank below ground under the house fed from the "utility" which will fill up by itself. Then pump from that up to the house. So you will not run out of water. BUT if you are at the top of the hill you may still need to "suck" the water to you.

    It is fun here isn't it?

  23. #23
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    Quote Originally Posted by hazz View Post
    Quote Originally Posted by ralphlsasser View Post
    I have a water pump that comes on every 30 minutes or so for just a second. I've checked for leaks several times and nothing is leaking. Any advice or comments would be greatly appreciated.
    Also, is it possible the pump could be loosing it's prime?
    I've found with an accumulated type pump, a slightly dripping tap can be enough to cycle the pump ever 30-180 minutes or so.

    One thing to bear in join with accumulated type pumps is in the majority of cases there is no membrane between the air and water in the tank. this means that over time the air dissolves into the water and the accumulator becomes less effective as reducing pump cycling for small water flows. its worth once a year or so, isolating the pump and draining the accumulator tank.

    If I were to buy a new pump I would probably look into the benefits of using a constant pressure pump with an inverter. has anyone had any experience with these? are they worth the extra money?
    I'm ignorant about pumps, but it looks like what we used to call a Bladder tank with a pump motor attached where air is at the top of the tank to push the water out. I may be way off base, but it looks the same.

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    The way it is piped, I'm not sure I can isolate the pump from the tank. I don't have an accumulator tank other than what's above the pump assembly.

  25. #25
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    This is an accumulator (or bladder, pressure, buffer etc-call it what you will but the correct term is accumulator) type pump. It stores a pressurised amount (head) of water in the tank underneath. The tank is seperated by a rubber membrane - on top is a pressurised air. When the tap is opened this pressurised air pushes down on the water giving instantanious pressure at the tap. The accumulator tank enables the pump to cope with a slow flow rate. Without an accumulator tank the pump would switch on and off very rapidly. Once the pressure drops the pressure switch cuts in starting the pump until the tap is switched off and the pressure builds up once again switching the pump off.

    This is your constant pressure pump.



    pretty similar to the accumulator pump except it doesn't have the tank underneath. Instead it has a very small accumulator built into the pump seen here at the back right of the picture. These pumps will cut in the moment you open a tap.

    The problem with both these pumps is that eventually you will lose the air pressure out of the accumulators. If your pump is cutting in and out like mad you may have to replenish the air pressure in the accumulator. This is not as easy as it sounds as it isn't like pumping up a bicycle tyre. It needs a fair amount of pressure and I am not sure how to get the correct amount in it but the best way is to turn the pump off, crack open a tap and let the water pressure drop. Then get a bicycle pump and give it a few pumps. Do not wheel your compessor over to it and give it a blast, you will rupture the membrane! The constant pressure ones are complete bastards as the tank is so small. Then get the pump on again and once it cuts out read the air pressure. You can use a tyre presure gauge but it is easy to lose the pressure again using one of those and back to square one. Being cheap bastards they don't include a pressure guage on the top of the accumulator but I would recommend doing that. Now, how much air pressure to put in I am not sure but I will try and find out. With a guage installed it is easy to see at a glance if you have pressure in your accumulator. If you lose this pressure you will get many of the problems people are describing here. The pump will cut in and out straight away and "hammer" at small tap openings as there is no "buffer" of air left to compress. Water doesn't compress so the pressure switch immediately cuts in and out through the pulsations in the water. Do not adjust the pressure swith unless absolutely nessecary! It is factory set and once you move it you have no idea at what setting it is at! That is why you will see that they have a dollop of stuff on the threads to stop it moving. Fiddling with that will cause plenty of problems! It is easy to install a pressure gauge on top of the accumulator and a shame they don't include one. Their reasoning is any problems call in a service tech who will do what I have described above but I hope that this will help solve some of the pump problems people are going to have and not have to get Somchai in to really screw it up for you. Obviously there are other problems to encounter the main being leaks upstream of the pump. Often they are installed poorly with cheap fittings. Buy good quality fittings! I also get bugged about how they install the with fixed, ridgid pipe so if you need to take it apart you need to cut it and reglue adaptors into it. Total PIA. I have not seen many options but a bolted flange or threaded coupling would be good.

    BTW, I stand to be corrected on any of the info above. I work with pumps a lot and is what I have learnt. I will try t find out moreabout replacing the air pressure into the accumulator.

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