How to Convert Flow Rate to Bar

There isn't a way of converting flowrate to pressure unless the characteristics of the system are known.

Try attaching a pressure gauge to the outlet and measure it.

If you can plug the flow with a pressure gage attached, you will get the static pressure of the plumbing system. If there is a way to attach a tee to the pipe with one leg going to the spout and the other with a pressure gage attached, you can get the flowing pressure. If this is low in comparison to the static pressure, you have some sort of obstruction upstream. Have you had the valve apart to see if it is OK?

I think fire departments have some approximation equations for estimating flow rate thru a given nozzle size with a given pressure. You have measured the flow rate, you can measure the pipe inside diameter, and calculate an approximate pressure.

Don't know how practical this is, but could you attach a hose to the exposed pipe and elevate the open end to about 30 feet / 10m above the connection? (It doesn't matter (within reason) how long the hose is or what route it takes). If so, turn on the supply - if water comes out of the end of the hose, you've got at least 1 bar.

Hmm, seems like pipe losses and local losses would be a consideration especially when using something like a water hose, but then again I am only a civil engineer.

How can you get significant pressure loss in 10m of hosepipe (with low flow rate) unless there's a leak ?

Agreed.

Pressure loss is not the issue here, flow rate is.

Standard 15mm pipe is used for sinks, handbasins & feeds to other low volume equipment - washing machines, toilet cisterns, etc.

Unless each is fed separately, these are taken from the feeder pipe, which is generally 22mm - this gives more than double the cross-section area, so can supply twice the volume (at least) than a 15mm pipe.

Victorian plumbing often had 1" (25mm) pipes leading to the bath, which allows a flow rate of almost 3 x that of a 15mm pipe for the same head pressure.

A little experiment, if you wish: measure the time taken to fill a barrel with water from a pressure washer, then repeat using just the hose. Which takes less time?

Unless the water is static you are going to have a head loss due to friction of the water moving through the pipe. With a low flow rate the loss might be relatively insignificant since losses are related to the square of the average velocity.

However that bring up the question of what is significant loss, since he is talking about an apparent reduced flow rate from a specific fixture. We might be talking about less than 5 psi of pressure difference between the flow rate he desired and what he is seeing. Since he really would not know the pressure with the water flowing out the end, as 1 bar is an estimate.

It is better to actually raise the hose util the flow is static and measure the static height of the water column. Then are no pressure losses due to friction and no estimates of pressure/orifice velocity at the end of pipe. of course you would need to elevate the hose to about 93 feet to achieve a static head equal to 40 psi.

If you read my post (to which you replied) you'll see that the hosepipe was proposed only to determine whether at least 1 bar (the min. rated working pressure of his spout) was available. In this case, flow rate does not come into it.

......or is the non-return valve in the fitting's cold line installed the wrong way round?

You might also want to check that the tap in the bathroom is not blocked with scraps of plumber's PTFE threading tape - this can be the usual reason in a new piping installation.

Also, what result do you get if one of the OK taps in another room is connected at the bath ?

Just wanted to say a bug thanks for all off your comments. Particularly like the one about attaching a 10M hose to the tap as reminds me of scuba diving lessons. Sadly no way to do this but a great idea.

Will try the other suggestions and let you know how I get on.

You could try using Bernoulli's principle to give you an estimate of the pressure in the boiler since you already know your flow rate and your pipe diameter. You can read on the method in Wikipedia and it should not be that hard to do the calculation.

Where are you? Apparently you use the metric system, so my reply may not help, because your threads may be totally different. In the USA I found I could screw a garden hose female fitting on a standard water pipe. Not a great fit, but it worked for a temporary connection. It was probably 3/4" iron pipe.

Greetings. We get this in my industry as well.

What I think they mean is "1 bar flowing pressure at the valve". Mount a gauge just in front of the tap and open it. The difference between static and dynamic pressures at your valve could be quite large.

Good Luck!

OK, I will throw my 2 cents in the hat here. There have been a number of good suggestions here, so hopefully this will fall into that category. Starting from the beginning, you indicate that you have good pressure everywhere but the tub spout. Have you tried running the bathroom sink (hot & cold on full) while running the tub? If there is no appreciable difference in the water flow at the sink, then you can narrow the problem down to the supply lines to the tub control, the control itself, or the piping after the control to the spout.

I am not sure about your area, but here in the States most all tub/shower control valves are anti-scalding and require both hot and cold water supplied to the valve in order for the valve to flow water correctly, so this might be a possibility. If that checks out OK, then turn off the water supply to the control valve and remove the valve out of the body and check for debris. Often times when a water system is worked on, debris can come loose and find its way to control valves creating blockage.

If all of this checks OK, then the assembly of the piping for the tub must be disassembled, starting at the spout and working backwards into the piping system until the blockage is found. The only reason you have no/low pressure is because an obstruction is blocking the water.

Let us know what you find. Good luck. This message will self destruct in 10 seconds. Sorry about that last one - a throw back to the days of Mission Impossible TV style. :)

Baths are usually supplied by 22mm plumbing (all the way from the tank) to give the flow rates required to fill them in a reasonable time.

I would like to add the following to your response. What is the connection size on this fixture ? Is the piping significantly reduced from the fixture back to the source/boiler ? IF yes, have it repiped with the same size as the fixture connection.

Probably 15mm inlet is too small for a waterfall spout. However a 11 litre/min flow should give more than a dribble. With the spout fitted do you still get 11 LPM?Does the manufacturer give a best flow spec?

Soemthing to consider here. The pipeline from the boiler to where it is distributed will burn some energy. This energy can show as pressure and/or flow rate seen at the outlet side of the system. You should tap a pressure gauge in immediately above the tank itself. Your spout burns some of the pressure energy converting it to velocity at each orifice on the spout. If you lack the energy (e.g. pressure in the system at the spout) you get reduced flow rates through the spout. You system pressure however, is usually based on the pressure at the street minus all the losses for the plumbing and elevation changes. The way to reduce the losses due to piping is to enlarge piping. To reduce local losses, have the fewest abrupt changes, turns or valves in the lines, etc.. to reduce elevation, well operate at a lower elevation on the outlet side (this would be hard to do). So you could be seeing either excessive losses due to plumbing in the lines and elevation changes. Larger strighter piping is ususally the easiest solution to excessive losses, or alternately different low flow fixtures (or live with the low pressure).

I have recently had a new pressurised boiler put in and it's been limited to 3 bar.

What does the boiler's pressure guage say? Do you actually get anywhere near 3 bar?

Has the main stopcock been fully opened after the installation?

Have you tried the old tap to see if the flow is as before?

rom Sleepy,

I had a similar problem, low flow, this was before i had my pipes changed in a Bathroom refit.

I then fitted a 3 bar pump and this improved matters.

And with the pipe refit, which , incidentally included large in line taps for maintenance and larger pipes and easier and fewer bends the fittings simple gush water.

I am sure that it could be better but seems OK to me!

This system actually feeds a shower in one room and a bath/shower in another quite satisfactorily.

i suspect that you either have a pipe problem, think bigger, think flow or a fixture problem,

As others have said do you have good flow from other fixtures?

Also do whatever tests that you can; the hosepipe one is good as all you need is a height measurement to calibrate the pressure!.

Very good Luck

Sleepy

Hi MattR,

Nice to see you publish this question in open forum, on a new thread. I told you it may make a difference but you have to be pleased with the replies?

As has been said there is no relation between flow-rate and Bar directly.

Can you give a little more detail on the supply to the bath room. You should have a minimum of 18-22 mm ID, then as you rarely have the bath taps on at the same time as the shower, the flow will be more than adequate. That is with the proviso the shower outlet, where the shower head is attached, is not several times the ID of the pipe supplying the shower/bathroom.

If you do not have a 18-22 mm ID pipe to supply water to the bathroom, then the plumber wants a little word in his ear, like: why the f- - - - - - - - !

Still a little short on info' here though. Is the Boiler or Heater in the bathroom, or is the bathroom three or more floors up from the level the boiler is fitted?

The back-flow as you call it will happen on any fountain or shower-head when it has a little water from it, and when the shower tap, or bath tap, if the shower is running from a third sprocket from the bath-tap, is not turned fully on, or as fast as you want, the external 'back-flow' will stop while in use, but it will still happen as you turn the shower off, always. You never usually notice it because the drip fall within the bath or show basin.

Ways round it are to have the shower moved over the bath slightly until the bath catches any drips.

Hang a short length of clear plastic so it catches any drips, and directs them into the bath.

Or, a quick and easy method that may sound wild but does work, is to perhaps use a gold or silver coloured thread or chain from the fitting, (but have in mind I know not what the fitting looks like shape-wise) allowing this to dangle and maybe if you are artistic, finished with a bow. Of course the colour and the bow are complete unnecessary, but they look good. I have seen this chain type flow director used on some outer building rain gulley's. The only difference is, they had 10 cm wide chain. At first glance, and if it was not raining, there was nothing to spoil the wonderful lined of the building, but they worked brilliantly when it rained, with apparently invisible rain pipes taking the gully water to ground drains.

Even if the shower head is several Cm's outside the edge of the bath, the water will run down the thread or rope or cable to be redirected into the bath, with no drips.

I will not repeat what I said in PM, as others here have covered it and confirm what I have said.

To finish, you must have an ample supply of water. This does not have any connection or correlation with pressure, as, if you are getting your water supply from the mains water running in (pipes outside and underground) the pressure will be more than ample to supply a shower fitted on the second or third floor. As the storey height on building is termed differently in the UK and the States, I am talking about a shower fitted on the first floor UK, or the Second floor USA.

The other thing usually necessary for a successful shower is enough head. The distance between the water outlet, and here it would be the shower, and the lowest point of the water feed from the Tank in the loft or roof-space. Your shower details will explain what head you need for your shower. As this amounts to little more than a metre or so, it is only usually a problem with low roofed houses and when you may want the shower-head to be fitted higher, maybe for the extra tall people.

Take care

bb