how do i measure my mains water pressure

[mbell]

Hi There, i am looking to measure my water pressure from my kitchen mains supplied tap. Can this be done by seeing how much water comes out in 1 minute? is there a special calculation also does the same apply if you measure it at different water outlets around the house.
Any help would be appreciated
Thanks
Mark

 

[mogget]

You're confusing the pressure with the flow.

The flow can be measured with a jug / bucket / timer and maths, as you suggest.

To measure the pressure you'll need a pressure gauge.

 

[mbell]

You're confusing the pressure with the flow.

The flow can be measured with a jug / bucket / timer and maths, as you suggest.

To measure the pressure you'll need a pressure gauge.

ok thanks however does the guage just fit onto the tap or is there more to do? do you just buy them from a Plumbing Shop?
also with regards to the flow rate i presume if you fill 13 litres in 1 minute your flow rate is 13 litres per minute! simple i guess however how does this then transform into the flow rate your combi outputs?

Maybe i am confusing it more but i am trying to get to the bottom of a terrible pressure on my shower and find ways to fix or make this better.

Any advise help is much appreciated

thanks

Mark

 

[Agile]

Many people seem to get very confused by pressure, flow and dynamic flow! There should be an FAQ about it.

You need a flow rate of 13 li/min absolute minimum whilst leaving a residual pressure in the pipes of say 0.5 Bar as there is a pressure loss within the boiler.

An open tap flow of 13 li/min will possibly reduce to 5-10 li/min dynamic flow rate at 0.5 Bar.

Furthermore most showers need at least 0.5 Bar to produce any useful jet flow through the orifices.

Tony

 

[mogget]

does the guage just fit onto the tap or is there more to do? do you just buy them from a Plumbing Shop?

I've never seen one that fits over the tap, such a thing may exist though, perhaps the proff's on here can provide some more insight?

If you've got an outside tap, or another tap with a threaded end (edit - washing machine tap?), you will be able to fit the gauge with an adaptor.

also with regards to the flow rate i presume if you fill 13 litres in 1 minute your flow rate is 13 litres per minute! simple i guess

It is that simple!

however how does this then transform into the flow rate your combi outputs?

There's two sides to this. First is how much water will flow through the boiler, second is how much the boiler will be able to heat. Combi's are usually quoted in litres per minute for a certain temperature rise. For example, your boiler might be quoted at 10 l/min for a 35 degree rise, that is at 10 l/min the water comes out 35 degrees hotter than it went in. If the flow increases, the temperature rise will be less (because there's only a set amount of heat available) and the water will be cooler.

Maybe i am confusing it more but i am trying to get to the bottom of a terrible pressure on my shower and find ways to fix or make this better.

Has the shower always been like this, or has something changed?

Is the shower valve thermostatic?

I'm assuming this is a normal shower, not a super duper hydro-bath-and-steam one.

It would be worth measuring the flow from the kitchen cold tap - depending on the flow, it may be possible to say whether the pressure is adequate without needing to buy a gauge.

 

[mbell]

does the guage just fit onto the tap or is there more to do? do you just buy them from a Plumbing Shop?

I've never seen one that fits over the tap, such a thing may exist though, perhaps the proff's on here can provide some more insight?

If you've got an outside tap, or another tap with a threaded end (edit - washing machine tap?), you will be able to fit the gauge with an adaptor.

also with regards to the flow rate i presume if you fill 13 litres in 1 minute your flow rate is 13 litres per minute! simple i guess

It is that simple!

however how does this then transform into the flow rate your combi outputs?

There's two sides to this. First is how much water will flow through the boiler, second is how much the boiler will be able to heat. Combi's are usually quoted in litres per minute for a certain temperature rise. For example, your boiler might be quoted at 10 l/min for a 35 degree rise, that is at 10 l/min the water comes out 35 degrees hotter than it went in. If the flow increases, the temperature rise will be less (because there's only a set amount of heat available) and the water will be cooler.

Maybe i am confusing it more but i am trying to get to the bottom of a terrible pressure on my shower and find ways to fix or make this better.

Has the shower always been like this, or has something changed?

Is the shower valve thermostatic?

I'm assuming this is a normal shower, not a super duper hydro-bath-and-steam one.

It would be worth measuring the flow from the kitchen cold tap - depending on the flow, it may be possible to say whether the pressure is adequate without needing to buy a gauge.

thanks for this info as i am not a plumber i kind of understand most of it and am learning everyday basically i had an old tanked in the loft system and then had a new combi boiler fitted the thermostatic shower is now terrible pressure and temperature control is rubbish in fact we have taken the temperature control of so it does not stop at the red button and we can gradually increase the temperature without burning ourselves.
My plumber tells me the shower has 3 to 3.5 bar pressure when he measured it but this was done after the new boiler was installed. I am told by my plumber to buy a new shower like a really top of the range mira for a more pressure and powerful shower. What keeps getting me mixed up is i had all of this with the shower i have which use to have a shower pump obviously the pump has now been removed and i just dont think the shower works the same anymore. In a previous thread i talked also about the refurb i am planning to my upstairs bathroom and want a really really powerful shower and have been advised that the second bathroom will need a unvented cylinder or mega flow but even with this someone advised me the pressure still may not be any better. It seems like a mine field and you find it hard to trust the people who come into your house as all they see is the labour intensive pounds in their pocket!
All advise you can give is a real help becuase I at least feel that I am armed with the correct information when the plumbers come around

thanks again

Mark

 

[mogget]

3 bar is a reasonable pressure, and should give a good shower if the combi is powerful enough - which boiler do you have?

That said, nothing will match a pumped shower for sheer drenching ability. I don't think an unvented cylinder would help, as the flow would still depend on the mains supply. You can install a conventional open vent cylinder with a combi if you want to have a pumped shower.

There are combi boilers that can cope with two showers, I suspect that probably wouldn't stretch to two really powerful showers.

I don't remember your previous thread, so I may have advised this before, but how good is the flow at the shower valve, with the hose and head removed?

 

[mbell]

3 bar is a reasonable pressure, and should give a good shower if the combi is powerful enough - which boiler do you have?

That said, nothing will match a pumped shower for sheer drenching ability. I don't think an unvented cylinder would help, as the flow would still depend on the mains supply. You can install a conventional open vent cylinder with a combi if you want to have a pumped shower.

There are combi boilers that can cope with two showers, I suspect that probably wouldn't stretch to two really powerful showers.

I don't remember your previous thread, so I may have advised this before, but how good is the flow at the shower valve, with the hose and head removed?

The new boiler i have is the potterton performa combi he 30kw.
I was told this was decent enough but am now being told that it cant cope with 2 bathrooms i have already noticed that if your in the shower and the upstiars toilet is flushed the pressure drops i guess i should have researched this part before hand

To be honest i am going to take a chance and buy a mira excel shower and have this fitted in place of the now dodgy shower downstairs and make do with this on the combi boiler however i need to get the new refurbed shower room upstairs running to a severe drenching level i want the shower to batter your body early in the morning! if you know what i mean. Any ideas help you can make would be much appreciated as I feel my plumber and myself have reached the end of the road discussing this matter!

Thanks Again

Mark

 

[Yukster]

I am also trying to measure flow and pressure to establish what mixer shower tap to get. I've got the water pressure gauge which fits a washing machine tap but I am not sure how to use it. I would appreciate if someone can answer the following questions:

When measuring flow rate and pressure, do i measure the cold water, hot water or both?

If I measure the flow rate liters/minute, would that be enough or do I need to ascertain the dynamic flow rate (can someone explain what it is?)

Do I need to measure the water pressure coming out of the the shower tap (hot and cold water taps fully open) or can/should I measure it elsewhere?

Thanks for your help

 

[Agile]

To be honest i am going to take a chance and buy a mira excel shower and have this fitted in place of the now dodgy shower downstairs and make do with this on the combi boiler however i need to get the new refurbed shower room upstairs running to a severe drenching level i want the shower to batter your body early in the morning! if you know what i mean. Any ideas help you can make would be much appreciated as I feel my plumber and myself have reached the end of the road discussing this matter!

Thanks Again

Mark

Apart from having a totally useless plumber, you seem to have far too much money to spend and far too little understanding of what your mediocre boiler and limited mains flow rate can do.

Tony

 

[TicklyT]

Connect pressure gauge to a cold W/M tap or outside tap, and turn that tap on. That will measure the static pressure. Your plumber suggests it should be about 3 Bar

With your gauge still connected, open another tap (say, kitchen tap) and note the new pressure reading with the tap running. That is a dynamic pressure, but it is meaningless without knowing the associated flow rate.

Time how long it takes to fill a bucket of known volume, and convert that time to a flow rate in litres per minute.

The second pressure reading and flow rate together give a meaningful dynamic pressure (eg 1.5 Bar @ 15 Litres per minute)

You can adjust the flow rate at the tap to whatever value you wish to know the dynamic pressure for, and measure the pressure, or repeat the test for a few random (but measured) flow rates, and compile a graph of pressure and flow rates (say 2.5 Bar @ 10 Litres / Minute, 2.8 Bar @ 5 litres / min)

You can repeat the above for the hot water system. Expect the dynamic pressure to fall faster, reflecting the additional restrictions through the boiler.

As a rule of thumb, water pressures in a first floor bathroom will be 0.2 to 0.3 Bar lower than in a ground floor kitchen. The difference is usually of little significance for mains pressure systems.

The way to get more out of the system than you put in is to restore the gravity system and pump your plumber has removed. The storage tank and hot cylinder act as buffers you can draw on for the duration of your shower.

The other way is to increase the input by upgrading your cold water supply and boiler. Just increasing the flow rate is useless if the boiler doesn't have the capacity to heat that much water.

 

[DeltaT2]

Connect pressure gauge to a cold W/M tap or outside tap, and turn that tap on. That will measure the static pressure. Your plumber suggests it should be about 3 Bar

With your gauge still connected, open another tap (say, kitchen tap) and note the new pressure reading with the tap running. That is a dynamic pressure, but it is meaningless without knowing the associated flow rate.

Time how long it takes to fill a bucket of known volume, and convert that time to a flow rate in litres per minute.

The second pressure reading and flow rate together give a meaningful dynamic pressure (eg 1.5 Bar @ 15 Litres per minute)

You can adjust the flow rate at the tap to whatever value you wish to know the dynamic pressure for, and measure the pressure, or repeat the test for a few random (but measured) flow rates, and compile a graph of pressure and flow rates (say 2.5 Bar @ 10 Litres / Minute, 2.8 Bar @ 5 litres / min)

You can repeat the above for the hot water system. Expect the dynamic pressure to fall faster, reflecting the additional restrictions through the boiler.

As a rule of thumb, water pressures in a first floor bathroom will be 0.2 to 0.3 Bar lower than in a ground floor kitchen. The difference is usually of little significance for mains pressure systems.

The way to get more out of the system than you put in is to restore the gravity system and pump your plumber has removed. The storage tank and hot cylinder act as buffers you can draw on for the duration of your shower.

The other way is to increase the input by upgrading your cold water supply and boiler. Just increasing the flow rate is useless if the boiler doesn't have the capacity to heat that much water.

There you are Tony, a concise & well thought through answer!! Stick that in your FAQs

 

[Yukster]

You can repeat the above for the hot water system. Expect the dynamic pressure to fall faster, reflecting the additional restrictions through the boiler.

Thank you very much for the clear a detailed answer. My only follow-up question is about connecting my pressure gouge to the hot water supply. the Gauge has a 3/4" connection. The showers outlet is 1/2". I've been trying to find a 3/4" male to 1/2" female adaptor which will enable me to connect the gauge to the shower outlet. Unfortunately, i couldn't find one. Any suggestions?

 

[megawatt]

Agile Wrote:

Apart from having a totally useless plumber, you seem to have far too much money to spend and far too little understanding of what your mediocre boiler and limited mains flow rate can do.

Nice to see nothing's changed here ... Tony still posting really helpful information

MW

 

[gco]

I needed to measure my water pressure as I was fitting a water filter with a maximum pressure rating, and I needed to know if my water pressure was within spec or if I would need to fit a pressure reducing valve. I found this thread whilst trying to find out how to measure water pressure without a gauge, but as it doesn't actually explain how to do this I thought I'd post the method I used.

You will need:
1. A bottle with a plastic screw cap. This needs to be able to hold pressure, so something that contained a carbonated drink is ideal. It needs to be clear enough for the liquid level to be visible. The larger and narrower the better. I used a 1 litre bottle that had contained sparkling water. The taller the bottle the more accurate the measurement is going to be.
2. A means of marking the bottle (e.g. a permanent felt-tip pen), or a scale on the bottle from which the level of liquid in the bottle can be accurately measured.
3. Measuring equipment, which can either be scales or a liquid measuring jug.
4. A length of hose pipe which is firmly attached to the water supply to be measured. Ideally attached via a manifold or some means of releasing pressure in the hose in a controlled way - see method step 8 below!
5. A roll of insulating tape (or similar).
6. A stanley knife (or other means of making a hole in the cap of the bottle).

WARNING: This process is not without danger. Please see subsequent post (2 down) and take appropriate precautions.

Method:
1. Make a hole in the screw cap that is just large enough for the end of the hose pipe to be pushed through. The tighter and better the fit the better. I found I could do this most easily working from the outside of the cap starting with two cuts made with a stanley knife at right angles to one another and then cutting out the four triangles, followed by a few adjustments. Be careful of your fingers! Push the end of the hose pipe through the hole so that it protrudes an inch or so into the bottle.
2. Wrap insulating tape around the very end of the hose pipe to increase its diameter so it's a snug fit in the neck of the bottle. This will create an enlarged end on the hose pipe that will prevent it coming out of the cap and will create a water seal (as the chances are the hole you made won't be a perfect fit for the pipe). In my case I took 20 turns of tape. Pull the hose pipe through (out of) the cap until the plug of insulating tape is firmly up against the inside of the cap.
3. Connect the hose pipe to the water supply.
4. Raise the end of the hose pipe and flush the hose so that it's completely full of water and there is no air trapped in it. Turn off the water but keep holding the end of the hose pipe up so it remains completely full of water.
5. Screw the bottle firmly onto the cap. The bottle will, of course, be upside down. Make a mental note of how much of the neck of the bottle is filled with hosepipe and water.
6. Turn on the water. Be cautious - slow is good. The water level in the bottle will rise and eventually stabilise. If you are using a carbonated drinks bottle and its bottom (the star-shaped bit) pops then turn off the tap immediately as (a) the pressure may be too high for this method to be safe and (b) in any case the measurement will be compromised by the change of bottle shape. The chances are that some water will be leaking from where the hose goes through the cap, but that doesn't matter. As the air in the bottle is compressed it will rise in temperature, which will affect the measurement (it will give you an under-reading of pressure), so give it a little time to cool down.
7. Whilst the water is still turned on, with the level stable and the air in the bottle not obviously warm, ensure that the bottle is absolutely vertical and mark the water level.
8. Turn off the water, release the pressure and unscrew the bottle from the end of the hose. This is where a bit of forethought will prevent you from getting absolutely soaked.
9. Turn the bottle the right way up and fill it to exactly the mark you made on the bottle. Measure the volume or mass of the water using a measuring jug or scales.
10. Fill the bottle with water so that it's almost full, with the exception of the bit of the neck that was filled with hosepipe and water in step 5. Measure the volume or mass of the water using the same units as in step 9.
11. Divide the larger measurement (step 10) by the smaller measurement (step 9) to give the total pressure in ata (atmosphere absolute) and subtract 1 to get the water pressure in atm (atmospheres), or bar to all intents and purposes.

In my case, my calculation was 1060/240 = 4.4 - 1 = 3.4 bar (or 50 psi).