Q. How to work out what pressure needed for house water pump?

[giddyup]

Mentioned here before, I have a Mitsu. WP205Q water pump that services our house. It's been in use for over 10 years and I need to replace it. I don't know the rating or pressure for this pump, but am wondering if I can downsize pressure-wise to a Mitsu WP105, which is about 2000 baht cheaper. Everything is at ground level, rarely more than one tap open at a time and perhaps lower pressure means less chance of a pipe bursting inside a wall. Opinions please.

[bankruatsteve]

If you need to save B2K and your old pump was more than enough, go for it. Sounds like a sensible choice. 

[DekDaeng]

34 minutes ago, bankruatsteve said:

If you need to save B2K and your old pump was more than enough, go for it. Sounds like a sensible choice. 

Fujika have a service - 'long motor' ???? - new pump & motor change for 2,000, for their 250 watt pump. 

 

Mitsu may have the same?

 

I would not go to a lower power, as that might mean your service life sig. reduced.

 

Chances of pipe bursting not high, IMHO - ????

 

Is the pressure or flow inadequate now? What has changed?

[Swiss1960]

Pump sizing for me has only one important factor: pressure I get in my rainshower... I want a waterfall and not a drizzle. A Mitsu 205 gives you this, a 105 probably not

[IvorBiggun2]

Get the most powerful you can afford. I guarantee you won't be disappointed.

 

https://www.lazada.co.th/products/walrus-1-750-tq800-i511010199-s907582748.html?spm=a2o4m.pdp.recommendation_2.1.60cfc017qFl10s&mp=1&scm=1007.16389.126158.0&clickTrackInfo=49fa7e4c-16c5-4f1d-b76e-77aac95bbd82__511010199__10100199__trigger2i__179586__0.267__0.267__0.10953969__0.0__0.013556659__0.0099544665__0__7__PDPV2V__250__null__74090130__0____12400.0__0.5008064516129032__5.0__1__6190.0__51053,54766,59383,65984,69806,72078,76899,82420,83677,85528__null__null__null__3650.16539

 

I recommend the TQ 800.

Edited September 4, 2020 by IvorBiggun2

[sometimewoodworker]

5 minutes ago, IvorBiggun2 said:

Get the most powerful you can afford. I guarantee you won't be disappointed.

Except when the pipes in the walls start blowing up. ???? 

[impulse]

6 minutes ago, sometimewoodworker said:

Except when the pipes in the walls start blowing up. ???? 

 

Typically, the maximum pressure isn't what changes.  That's determined by the diameter of the impeller.  It's the flow rate that changes because the impellers have wider vanes for more flow.  Of course, that requires more power, so a bigger motor.

[sometimewoodworker]

21 minutes ago, impulse said:

 

Typically, the maximum pressure isn't what changes.  That's determined by the diameter of the impeller.  It's the flow rate that changes because the impellers have wider vanes for more flow.  Of course, that requires more power, so a bigger motor.

You are rather behind the times. My, not unusual pump can vary it’s output from 22psi to 80psi 

 

also the Mitsubishi pump pressure varies depending on the pump you get or adjustment you make, most other makes have the same variation 

Edited September 4, 2020 by sometimewoodworker

[impulse]

20 minutes ago, sometimewoodworker said:

You are rather behind the times. My, not unusual pump can vary it’s output from 22psi to 80psi 

 

also the Mitsubishi pump pressure varies depending on the pump you get or adjustment you make, most other makes have the same variation 

 

Not really behind the times.  Centrifugal pumps have run the same way for hundreds of years... 

 

Here are the pump performance curves- which are very useful- more so than the advertising hype. From size 205 and above, shut-off head (that's the maximum head at zero flow) is around 50 meters.  That tells me the impeller diameter is the same if they all have a single impeller.  The variation is the flow rate, which tells me that the impeller vane width is the variable factor.   The 85, 105 and 155 all have a similar shut off head at appx 35 meters, indicating they have a smaller impeller diameter than the bigger pumps.

 

In the case of the OP, deciding to go with a 105 would reduce the maximum pressure, and I'm not sure that will meet his expectations.

 

It's likely they have pressure relief valves and/or pressure shut-off valves to adjust the maximum pressure.  But the pumps themselves operate according to well established laws.   

 

Edit:  BTW, 50 meters of head is right at 70 PSI.  35 meters of head is 50 PSI.  The formula is meters x 3.28 x .433 for pumping fresh water.

Edited September 4, 2020 by impulse

[sometimewoodworker]

12 minutes ago, impulse said:

Not really behind the times.  Centrifugal pumps have run the same way for hundreds of years... 

 

Here are the pump performance curves- which are very useful- more so than the advertising hype.

As I said behind the times.

here are the performance curves from my pump

 

While invented in the late 17th century the technology has hardly remained the same, as shown above.

[Nero Dog]

I am using the WP-155Q5 (150W).

Two bedroom house, two toilets / showers. 

Had it 4 years, no issues. 

Good buy for about 5000 baht. 

[DekDaeng]

19 hours ago, sometimewoodworker said:

Except when the pipes in the walls start blowing up. ???? 

Water pressure is determined by the pressure switch setting.

[sometimewoodworker]

37 minutes ago, DekDaeng said:

20 hours ago, sometimewoodworker said:

Except when the pipes in the walls start blowing up. ???? 

Water pressure is determined by the pressure switch setting.

Or setting on the pump. And your point is?

 

My statement referred to the suggestion that you should use the biggest pump you can. This is poor advice and can lead to pipe failure.

[DekDaeng]

3 hours ago, sometimewoodworker said:

Or setting on the pump. And your point is?

 

My statement referred to the suggestion that you should use the biggest pump you can. This is poor advice and can lead to pipe failure.

the 'setting on the pump' is the pressure switch setting. 

I can't say pipes bursting in the walls is impossible, but I have never heard of it. My pressure is set at 36 psi - & that is good for 5 floors including a roof garden. 1" PVC is good for 450 PSI so a fair factor of safety there. Unless the joint was made badly - (very) 

 

Do you have experience of pipes bursting, from pump pressure?

 

PS it doesn't matter what size (power) pump you put in, the power will be cut as soon as the pressure reaches the switch set point.

It might help to have a reservoir tank at the end of your line to dampen any hydraulic shocks - also gives 'immediate water' when you turn on any tap -

 

Edited September 5, 2020 by DekDaeng

[sometimewoodworker]

32 minutes ago, DekDaeng said:

the 'setting on the pump' is the pressure switch setting.

Not on my pump it’s variable as I showed in the pictures above (22psi to 80psi), neither is it on the inverter pumps by Mitsubishi and hitachi 

 

36 minutes ago, DekDaeng said:

I can't say pipes bursting in the walls is impossible, but I have never heard of it.

Pipe in the wall usually have enough UV protection, but yes I’ve has a pipe go brittle and burst. That is why I almost always use 13.5 pipe now.

40 minutes ago, DekDaeng said:

PS it doesn't matter what size (power) pump you put in, the power will be cut as soon as the pressure reaches the switch set point.

Of course but the bigger the pump the higher the set point is unless you have an inverter when it’s variable by the user.

[billd766]

On 9/4/2020 at 8:24 PM, sometimewoodworker said:

Except when the pipes in the walls start blowing up. ???? 

You can always put a shut off valve both before and  after he water pump. That way you can alter the flow of water into the pump and the output pressure going to the house.

 

Thathas the advantage of isolating the pumpif you ever need to replace it as you have to now.

[sometimewoodworker]

11 minutes ago, billd766 said:

You can always put a shut off valve both before and  after he water pump. That way you can alter the flow of water into the pump and the output pressure going to the house.

 

Thathas the advantage of isolating the pumpif you ever need to replace it as you have to now.

The cutoff pressure is not changed by that you would just drop the flow. Anyone with sense will have valves that can isolate the pump. 
 

Why do you think I need to change my pump?

[topt]

2 hours ago, sometimewoodworker said:

The cutoff pressure is not changed by that you would just drop the flow. Anyone with sense will have valves that can isolate the pump. 
 

Why do you think I need to change my pump?

Perhaps he has something against Grundfoss............

[sometimewoodworker]

7 hours ago, topt said:

Perhaps he has something against Grundfoss............

And it seems he doesn’t know about pressure limiters .

[DekDaeng]

On 9/5/2020 at 9:27 PM, sometimewoodworker said:

Not on my pump it’s variable as I showed in the pictures above (22psi to 80psi), neither is it on the inverter pumps by Mitsubishi and hitachi 

 

Pipe in the wall usually have enough UV protection, but yes I’ve has a pipe go brittle and burst. That is why I almost always use 13.5 pipe now.

Of course but the bigger the pump the higher the set point is unless you have an inverter when it’s variable by the user.

Normal pump / normal switch is variable by the user, too; there is a grub screw in the centre of the top of the switch - (under the cover) screw it down for higher pressure, up for lower. Not too much. ????

[keithkarmann]

On 9/5/2020 at 8:44 PM, DekDaeng said:

the 'setting on the pump' is the pressure switch setting. 

I can't say pipes bursting in the walls is impossible, but I have never heard of it. My pressure is set at 36 psi - & that is good for 5 floors including a roof garden. 1" PVC is good for 450 PSI so a fair factor of safety there. Unless the joint was made badly - (very) 

 

Do you have experience of pipes bursting, from pump pressure?

 

PS it doesn't matter what size (power) pump you put in, the power will be cut as soon as the pressure reaches the switch set point.

It might help to have a reservoir tank at the end of your line to dampen any hydraulic shocks - also gives 'immediate water' when you turn on any tap -

 

Pipes leak in the wall when they have been incorrectly glued together.

[brianthainess]

Having asked this question on Lazada they only gave me the flow rate at about 40 ltrs a minute the pressure they quoted was 220volts LMFO.

[Elkski]

On 9/4/2020 at 8:28 AM, sometimewoodworker said:

As I said behind the times.

here are the performance curves from my pump

 

While invented in the late 17th century the technology has hardly remained the same, as shown above.

The Scala2 is a booster pump.  It has a  high pressure setting like most pumps for a house.    It varies how  much pressure it adds a variable  amount to maintain a fixed "set" pressure.   

I see lots of misinformation about pumps here.  

Size of pump can mean many things.  But two main numbers are max head and flow rate, a third is max suction  head (how high can the inlet lift) .  I assume  you have positive inlet pressire via a tank.  Head is similar to Voltage. Higher voltage  = more flow or current.   Max head is how high can you  raise the hose until the flow stops.   Its a curve so if the pump only need to pump up 3 meters to the shower head you look  on the chart at 3 meters head and that is the max flow rate.   This doesn't take in account pipe size, length of pipe, and number of turns.   You need to add this pipe loss to showef head height above the pump. 

Most pumps have a pressure switch that cuts the pump off  when it gets to a set or adjustable pressure.  In the case of the scala2 is doesnt even run if city pressure meets its min  setting.  But if city pressure drops below the "setpoint it turns on and tries to keep the pressure constant.   It is a variable pump so it won't be cycling on and off like most pumps.  Which  brings us to pump size.  A pump which has higher flowrate or max head will not send any higher pressure to the pipes in the wall than the set point.   Unless we are talking about something monstrously oversized that the pressure cutoff switch cant react fast enough for.   

Looking at the 205q specs it is 38 lpm at  16 m head, and its switch seems fixed at  pressure settings of 2.8/2.1 kg/cm2.   OFF/ON

The 155 is a lower pressure switch at 1.9/1.3 kg/cm2. And flow of 30 lpm at 12m head.  

I think the 105 may be to  small.  How often does your 205 turn on and off when someone is showering?   What % of the max flow do you like?  Most shower heads are 1.8-2.5 gpm. Or 10 lpm max .   55 psi is enough to run  all my shower heads at the same time 42 lpm but the pupe run  is 3/4" PEX and only a 30' side run.  With maybe a 60' total from pressure regulator.  Many  shower valves like Grohe specify 55 psi.  I have 120 psi city p to work with.   

There are charts or formulas to convert size of pipe runs into head.    It is sorta trial  and error when you don't have the exact pipe drawings to work with.   

What is the  inlet source?  Inlet pressure makes a difference.  A storage tank with  fill switch is much better constant inlet supply pressure than straight on a city supply line. 

Do ti have a pressure  guage to read when pump if off (max pressure) and then read it with shower or kitchen faicet wide open.   See what pressure it operates at currently  for a flow rate you like. 

Measure how much water your using at your favorite setting.  You will need a pump with a curve that has a pressure flow rate you like.  What I'm saying if your  preferred shower flow valve  setting is wide open you won't like a smaller pump.   

Try to draw a pipe size and length diagram to the shower then convert to head loss and see if the 155 will work. 

Here is a pipe  head calculator. 

https://pentairaes.com/pump-calculator

  

Edited September 9, 2020 by Elkski

[chilly07]

We installed a higher pressure Mitsubishi and then had to replace many taps hoses and shower heads and repair other leaks. Next time we will size the pump more carefully.

[cjinchiangrai]

On 9/4/2020 at 9:18 PM, IvorBiggun2 said:

Get the most powerful you can afford. I guarantee you won't be disappointed.

 

https://www.lazada.co.th/products/walrus-1-750-tq800-i511010199-s907582748.html?spm=a2o4m.pdp.recommendation_2.1.60cfc017qFl10s&mp=1&scm=1007.16389.126158.0&clickTrackInfo=49fa7e4c-16c5-4f1d-b76e-77aac95bbd82__511010199__10100199__trigger2i__179586__0.267__0.267__0.10953969__0.0__0.013556659__0.0099544665__0__7__PDPV2V__250__null__74090130__0____12400.0__0.5008064516129032__5.0__1__6190.0__51053,54766,59383,65984,69806,72078,76899,82420,83677,85528__null__null__null__3650.16539

 

I recommend the TQ 800.

That would be incorrect. The power in a pump is split between flow volume and pressure. You need to look at the pump curve to see how the exchange works for a given pump.  A larger motor does not get better performance if it is oversized to the demand.  

 

For a single floor house the smaller pump should be OK though. I would look for about 3-5 bar peak pressure.  No way do these pumps blow properly sized pipes.

 

[sometimewoodworker]

2 hours ago, Elkski said:

The Scala2 is a booster pump.  It has a  high pressure setting like most pumps for a house.    It varies how  much pressure it adds a variable  amount to maintain a fixed "set" pressure.   

I see lots of misinformation about pumps here.  

Size of pump can mean many things.  But two main numbers are max head and flow rate, a third is max suction  head (how high can the inlet lift) .  I assume  you have positive inlet pressire via a tank.  Head is similar to Voltage. Higher voltage  = more flow or current.   

The SCALA 2 Is similar to most domestic pumps in that it has an ability to water supply from shallow wells (< 8 m) though it can accept a Max. inlet pressure: 6 bar. And from that it can supply water at the pressure you set on the pump from 1.5 bar to 5.5 bar variable in .5 bar increments. 

[Matzzon]

On 9/4/2020 at 1:33 PM, giddyup said:

Everything is at ground level, rarely more than one tap open at a time and perhaps lower pressure means less chance of a pipe bursting inside a wall. Opinions please.

Why would a pipe burst. Todays water pumps have both a regulator for pressure depending on the flow, as well as a shut off mechanism when you close the tap.

[sometimewoodworker]

34 minutes ago, Matzzon said:

Why would a pipe burst.

Old degraded PVC too much pressure.

 

35 minutes ago, Matzzon said:

Todays water pumps have both a regulator for pressure depending on the flow, as well as a shut off mechanism when you close the tap.

They do but that’s irrelevant if the pipe bursts, isn’t it?

[Matzzon]

8 minutes ago, sometimewoodworker said:

Old degraded PVC too much pressure.

 

They do but that’s irrelevant if the pipe bursts, isn’t it?

If the pipes are told old, the only sensible thing is to do a pipe replacement. The safety is there to prevent pipes from bursting. I thought you would understand that as you are so very well versed in construction. However, I was mislead of your previous amount of recommendations. 

[RocketDog]

I replaced a rusting old style pump with a small pressure tank with a 'constant flow type'. Several models are available with various pressure ratings set by a pressure switch. 

I got the increased pressure I wanted for the shower but neglected to think that the sink faucets would have a higher pressure too. 

I should have put valves in the sink feeds to adjust the pressure so that a full tap didn't splash out of the sink when fully on. 

Something to consider.