water pump: next to house OR tank?

[BritManToo]

24 minutes ago, Andrew Dwyer said:

From what I see of new house builds the pvc is always laid under the house slab , poorly assembled and use of glue is optional.

2 years after moving into a new house it developed a water leak underneath the house. After some serious investigation I found the leak was somewhere under the house and had no option other than running all new pvc externally .

Yes, my home too ......... but if any of it leaked I'd just drill through the outside wall, and cut out the interior piping. Just because the guys that built my house were half wits, doesn't mean I have to copy them. PVC pipe is very east and cheap to DIY, tiles and concrete are a bit beyond what I'm prepared to do.

[Old Croc]

20 hours ago, STD Warehouse said:

Tank been there for 30 years, back when there was not really electricity in this area, so they raised it to get a semi decent flow to the old bungalows that were previously here

If the tank worked OK without a pump when new, why is the flow so bad now?

Perhaps what's needed is for the 30yo pipes to be replaced.  A pump may not be necessary.

[Dazinoz]

20 hours ago, STD Warehouse said:

seems like theres no common consensus here. some say by the tank, some say by the house.

 

I guess if next to the house,  the pump is being forced to "suck" water from a source 120m away, which seems wrong and they are called pumps not sucks., my 2 cents

 

Lots of opinions but seems to be little advise based on facts.

 

I worked in the generating area of a large power station for 10 years and also an oil refinery 23 years and have operated many pumps over that time. The larger percentage of pumps are located as close as possible to the suction supply. As someone else has said this is done for a reason. You will often see suction supply lines larger than the discharge for the very reason of cavitation of the pumps from lack of suction supply. 

 

Pump best at tank.

[Artisi]

38 minutes ago, sandyf said:

The water pressure from the tank will be the same anywhere along the supply line.

You should give over with the scaremongering, and more consideration given to reality. Cavitation is an extremely unlikely event in a domestic water pump scenario. It is effectively caused by bubbles in the flow normally created by something in the water that has overheated and evaporated, such as a cooling agent. Completely different to getting air in the pump.

I have 3 of these pumps and look after 2 others. My Mitsy sucks the water out of an underground septic tank onto the garden. I do that for about 15 minutes every day. Quite often I forget to switch it off and it empties the tank and starts sucking air, quite often the pump overheats and the thermal trip cuts out. Been doing that a couple of times a month for the last 12 years without a problem.

Towards the end of every dry season as the well level gets close to the valve the pump starts to suck air, you have to wait for the well to replenish, bleed the pump and start again. Happens several times every year and has done so for the last 9 years without a problem.

When the pump starts to suck air you get a few large bubbles, not millions of small ones, and the pump stops pumping, there is no cavitation.

The problem is for the OP to make his own mind up and do what he considers best.

A few points needed for clarification to suit the physics of pumping / pumping systems:

 

1.Water pressure without flow at any point of the supply line will be the same , however once flow commences, the pressure will drop by the amount of friction head loss from the source to the point of measurement. The friction loss depends on pipe diameter, roughness, fouling and the flowrate.

 

2. Cavitation has nothing to do with entrained air or gas -  yes, a pump can stop pumping due to excessive air collecting in the impeller eye - that is not cavitation.

 

3.Cavitation is the function of NPSHa being less than NPSHr (Net Positive Suction Head,  a= available, r = required).

 

In simple terms, NPSHa is the result of atmospheric pressure on the supply source, plus or minus the water level in relation to the impeller eye and minus all friction losses due to flow.

 

NPSHr is a function of the pump design and varies depending on pump speed and flow.  

 

the noise from a truly cavitating pump is unmistakeable, and is completely different from the noise generated from entrained air (if any noise) 

 

For interest - pump cavitation is sometimes quietened by bleeding a small amount of air into the pump suction line, this has the effect of softens the violent  explosive noise (and damage) by absorbing some of the energy of the cavitation bubbles imploding back into solution.  

 

so endeths todays lesson of pump hydraulics 101.  ????

[Dazinoz]

10 minutes ago, Artisi said:

A few points needed for clarification to suit the physics of pumping / pumping systems:

 

1.Water pressure without flow at any point of the supply line will be the same , however once flow commences, the pressure will drop by the amount of friction head loss from the source to the point of measurement. The friction loss depends on pipe diameter, roughness, fouling and the flowrate.

 

2. Cavitation has nothing to do with entrained air or gas -  yes, a pump can stop pumping due to excessive air collecting in the impeller eye - that is not cavitation.

 

3.Cavitation is the function of NPSHa being less than NPSHr (Net Positive Suction Head,  a= available, r = required).

 

In simple terms, NPSHa is the result of atmospheric pressure on the supply source, plus or minus the water level in relation to the impeller eye and minus all friction losses due to flow.

 

NPSHr is a function of the pump design and varies depending on pump speed and flow.  

 

the noise from a truly cavitating pump is unmistakeable, and is completely different from the noise generated from entrained air (if any noise) 

 

For interest - pump cavitation is sometimes quietened by bleeding a small amount of air into the pump suction line, this has the effect of softens the violent  explosive noise (and damage) by absorbing some of the energy of the cavitation bubbles imploding back into solution.  

 

so endeths todays lesson of pump hydraulics 101.  ????

A very good description but hasn't answered the question for a non technical person where the pump should go.

 

We used to have an alarm on on our boiler feed water pumps on NPSH. They were BIG pumps. 30 years ago and cant remember all details but the electric motors were 3 phase 11,000v and 9000HP. Pumps would develop over 20,000kpa and a rated flow of 410kg/second. 

[toolpush]

You state that your current tank is supplied from a well. My question is this: type of pump and what is the rated flow rate, motor horsepower and depth of the pump in the well if it is a submersible pump? 

If you have a submersible pump in the supply well, I would recommend simply purchasing a reasonably sized accumulator tank and foregoing purchasing another water pump at all. Let the submersible well pump feed the accumulator tank and your house.

[Artisi]

8 minutes ago, Dazinoz said:

 

Lots of opinions but seems to be little advise based on facts.

 

I worked in the generating area of a large power station for 10 years and also an oil refinery 23 years and have operated many pumps over that time. The larger percentage of pumps are located as close as possible to the suction supply. As someone else has said this is done for a reason. You will often see suction supply lines larger than the discharge for the very reason of cavitation of the pumps from lack of suction supply. 

 

Pump best at tank.

you are correct in saying that the majority of pumps are located close to the source and for a good reason, the reason being  you only have the benefit of atmospheric pressure to "push" the pumped product into the impeller eye plus it's more economical - this is the norm - BUT, that doesn't mean the pump has to be located close to  the source - a large enough supply line resulting in low friction loss over its length will in theory allow a pump to be located where ever it suits you - but as I said economics rule .

[Ralf001]

1 hour ago, crazykopite said:

 the ones sold in Thailand are rubbish and are always troublesome mine is German made

 

 

 

Hate to be the bearer of bad news but that pump is made locally, Steibel Eltron have a manufacturing facility in Ayuthaya.

[Dazinoz]

4 minutes ago, Artisi said:

you only have the benefit of atmospheric pressure to "push" the pumped product into the impeller eye

Not always true. Many of the pumps in the oil refinery had a lot of pressure supplying them. Several thousand kpa in some instances when dealing with butane and propane (obviously in liquid form). Also the boiler feed water pumps in the power station I mentioned were supplied from a large pressure tank (the deaerator) high up in the structure but also had a steam supply to it in which the pressure could be increased if the NPSH came into alarm low.

 

And interesting sideline was a couple of pumps at the refinery pumped at relatively low pressure but the heavy hydrocarbon is was pumping was around 360 degrees centigrade. Interesting pumps to operate.

[Artisi]

7 minutes ago, Dazinoz said:

A very good description but hasn't answered the question for a non technical person where the pump should go.

 

We used to have an alarm on on our boiler feed water pumps on NPSH. They were BIG pumps. 30 years ago and cant remember all details but the electric motors were 3 phase 11,000v and 9000HP. Pumps would develop over 20,000kpa and a rated flow of 410kg/second. 

That's a big mother of a pump, wonder if they got their technical advice from Thai Visa Forum ???? 

 

I wasn't trying to answer the question on where the pump should go - I made my suggestion on that much earlier, this latest post was an effort to educate and turn-off some of the incorrect information posted on pump hydraulics. --  ie,. suck, push, cavitate, air, gas etc. 

Have been involved in the pump industry for over 60 years, so seen and been involved in most of it.  

[Ralf001]

1 minute ago, Artisi said:

 

Have been involved in the pump industry for over 60 years, so seen and been involved in most of it.  

 

do you feel they ones that suck are better than the ones that blow ?

[Artisi]

4 minutes ago, Dazinoz said:

Not always true. Many of the pumps in the oil refinery had a lot of pressure supplying them. Several thousand kpa in some instances when dealing with butane and propane (obviously in liquid form). Also the boiler feed water pumps in the power station I mentioned were supplied from a large pressure tank (the deaerator) high up in the structure but also had a steam supply to it in which the pressure could be increased if the NPSH came into alarm low.

 

And interesting sideline was a couple of pumps at the refinery pumped at relatively low pressure but the heavy hydrocarbon is was pumping was around 360 degrees centigrade. Interesting pumps to operate.

You're correct about pressure boosted pumps but splitting hairs here, I doubt any pumps being used by members posting here are pressure feed - unless it's a booster system and this thread is about atmospheric installed water pumps anyway ???? 

[KannikaP]

21 hours ago, STD Warehouse said:

2 bathroom taps

2 toilets

2 toilet spray guns

1 bathtap

2 showers with cold inlet

2 100L water heaters (for 2 bathrooms)

1 kitchen sink tap

1 dishwasher inlet tap

 

any recommendations of which Mitsubishi pump to buy? they have so many its confusing

And how many of those outlets will be used simultaneously?

[Dazinoz]

3 minutes ago, Artisi said:

That's a big mother of a pump, wonder if they got their technical advice from Thai Visa Forum ????

Yep, I remember talking to the manager of the power station one day and he said they were at a loss as to where to site the pump but then  discovered TVF and got all the info they needed.

 

As another sideline, that mother of a pump, well we actually had 3, 2 to supply full load flow and a spare, were started DOL (direct on line). That used to make the lights dim even at the power station.

[Artisi]

5 minutes ago, Ralf001 said:

 

do you feel they ones that suck are better than the ones that blow ?

depends who or what you are discussing ????

[ronaldo0]

I would put the pump near the house . The pressure of the tank being raised will give the pump a constant water supply through gravity providing there is water in the tank I would assume. Plus if there are any problems with the pump not cutting out etc and constantly running due to a fault or power supply being low then you won’t really know for a while and you have to go check it . My pump is just out the back of the house and when it has a problem with no water in it or not cut off due to electric being low I can hear it constantly running most of the time when I go into the bathroom . If it is 100m away the pump could be running for hours overheating and you wouldn’t know .

[ardsong]

Indeed a 4 M. high tank cannot bring a proper pressure at 100 meter plus distance.

 

there is only one good place for the pump and that is as close to the tank as possible. A pump is far better in pumping a high outlet pressure than in sucking a low inlet pressure, that could cause cavitation (the noise like there are running pebble through the pipe) that will damage your pump internals and maybe the outlet pipe.

[bradiston]

1 hour ago, crazykopite said:

First thing you need is a good pump most of the ones sold in Thailand are rubbish and are always troublesome mine is German made the price has come down considerably since I purchase it at home pro the furthest tap from the pump is 70 metre and I can tell you the power of the water is amazing so I’m sure it would suit your problem it’s also super quiet personally I would have it by the tank here are a few pics of the pump I’ve had this for a good 3 years+ never ever an issue it’s completely weather proof I thing I paid 9,000 but as I said tge price has come down a lot and it’s a brilliant pump it even has a pressure gauge within the housing .

Grundfos, all day, every day

[Dazinoz]

6 minutes ago, Ralf001 said:

 

do you feel they ones that suck are better than the ones that blow ?

I got distracted there for a bit. My lady friend does very little of one but does blow my money away fast.

[Artisi]

2 minutes ago, KannikaP said:

And how many of those outlets will be used simultaneously?

there are tables / references available that discuss the pump demand  based on the number and types of outlets - luckily this is a very low demand requirement unlike a 500 room hotel ????

[whaleboneman]

21 hours ago, sandyf said:

If the supply is restricted then that has been the problem all along and would need addressing wherever the pump.

if the pump is near the house he would soon be aware if there was cavitation.

and then what? move pump back to tank?

[The Theory]

A pump with pressure switch will function much better if it is near the house (and since the tank is raised the pump could be installed anywhere). The pipe size from the tank to the pump must be same or larger than the inlet size of the pump. From pump to the house as well. 

[whaleboneman]

2 minutes ago, The Theory said:

A pump with pressure switch will function much better if it is near the house (and since the tank is raised the pump could be installed anywhere). The pipe size from the tank to the pump must be same or larger than the inlet size of the pump. From pump to the house as well. 

My pump is at the bottom of the well, a long way from the house. It's been working quite well since 1972.

[JAS21]

21 hours ago, Rookiescot said:

OK I had a think about this and after over 20 years of working in chemical factories with storages and delivery pumps I cannot recall a single one which had the pump at the end of the line.

Every one had the pump located as close as possible to the supply tank bottom outlet.

Has to be a reason for that.

Of course you should locate the pump where it will get the maximum  suction head.

 

Anyone who suggests otherwise……

[The Theory]

7 minutes ago, whaleboneman said:

My pump is at the bottom of the well, a long way from the house. It's been working quite well since 1972.

Your pump is a "submerged" pump and turns on/off by the tank sensor. Not by pressure switch. 

[brianthainess]

22 hours ago, STD Warehouse said:

im going to buy a pump as the pressure is feeble in the house taps and shower

Don't really matter, but I fitted mine near the house to save laying more electric cable, the advantage for me is that I can turn the pump off from my switch board inside the house when need be. An example; pump running constantly and heard from house bcoz tanks 3,000.ltr were empty, the town water which feeds them must have been off for days . When town pressure is good I can turn off the pump easily. edit my town supply also runs through the pump.

[Bigz]

Do you get enough water throughout the year from the mains? Is the tank always full? 

I had a tank and a pump installed a few years ago only to realise that in the dry season they only turn on the water a couple of times a week for a few hours. It wasn't enough to fill my tank and half of the week I was out of water. So it turned out that it was a complete waste of money and had a borehole drilled instead.

[RocketDog]

22 hours ago, Neeranam said:

Why is the tank raised? You shouldn't need that if you have a pump.

Raising a tank may be problematic and/or expensive, but provides proportionally higher pressure to the pump, which saves pumping energy. Probably not enough to notice though.

[brianthainess]

1 minute ago, Bigz said:

Do you get enough water throughout the year from the mains? Is the tank always full? 

I had a tank and a pump installed a few years ago only to realise that in the dry season they only turn on the water a couple of times a week for a few hours. It wasn't enough to fill my tank and half of the week I was out of water. So it turned out that it was a complete waste of money and had a borehole drilled instead.

Sometimes the water is turned on at night, so I fitted another bigger tank.

[RocketDog]

22 hours ago, Neeranam said:

Why is the tank raised? You shouldn't need that if you have a pump.

Electrical conduit is cheaper and easier to run to the tank than large diameter pump inlet pipe.

 

This is my sprinkler system, not domestic water, and the yellow thing is a 2" solenoid valve to prevent leakage into the sprinkler system through the centrifugal pump.

The pump itself is in the plastic bin housing to prevent weather damage.

 

Lots of fittings to allow easily removal of the valve and pump for service.

 

These are well worth the additional cost, and service is something very few Thai installations even consider. The far future for them is tomorrow.