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Fire Sprinkler System Pressure Gauges

How to Measure Water Pressure for Sprinklers

Fire sprinkler water pressure
Hydraulic Fire Sprinkler System installaion outside of a building connected to city water supply

We are often asked by our customers: what are the fire sprinkler system pressure requirements and, what would be the maximum pressure for the fire sprinkler system be?

So, this simple article has been compiled as an aid to understanding the importance of the static sprinkler system pressure and the water flow combined with the dynamic pressure when considering the possibility of utilising the existing town mains water supply to the building or the buildings existing boosted cold-water supply.

The maximum water pressure is generally less important than assessing the minimum pressure for fire sprinkler system in the town main or, the duty of the booster pump that is providing the pressure and flow for the fire sprinkler system pressure requirements. A high pressure rarely causes a problem for a designer whereas a low pressure frequently does.

It is important to appreciate the fact that the dynamic water pressure and flow is generally not as important a factor when considering a Mist Sprinkler System for a residential property and that a Mist fire sprinkler system pressure can be obtained from a 25mm shared incoming water supply.

Residential Fire Sprinkler System Pressure

A typical residential fire sprinkler system pressure for a 4-bedroom house could be around 3 bar when measured at the point of entry within the dwelling and a typical fire sprinkler system pressure for a high-rise block of flats could be around 2.5 bar on each floor.

While the pressure requirements for a small 2 storey townhouse close to the town main could be as little as 2 bar measured at the point of entry however there are often very high dynamic pressure losses introduced by water companies like domestic water meters and stop cocks etc which reduce the maximum pressure for fire sprinkler system availability.

Consequently, while there may be 4.5 bar static pressure in the town main, the dynamics of the system between the town main and the entry point in the house will be considerable.

It is important to understand the difference between dynamic pressure and static pressure when deciding how much pressure for fire sprinkler system design is required. The simple explanation of static pressure of a system equates to the latent pressure in the system when no fluid is flowing. For example, a static pressure reading can be taken using a pressure gauge connected to an outside tap when there is no running water within the premises. However, this has little to do with the dynamic sprinkler system pressure.

The dynamic fire sprinkler system pressure for a residential sprinkler system is measured at a given flow of water typically, around 120 litres per minute (LPM) for a category 1 or 2 system and 240 litres/minute for a category 3 system. It is important to understand that these figures are irrelevant without knowing what the dynamic pressure equates to at the given flow of water.

Dynamic pressure could be thought of as a function of the flow of water and the losses that the flow encounters.

How to establish the minimum water pressure for the fire sprinkler system to work correctly?

The maximum water pressure requirement for the fire sprinkler system will be dictated generally by the water pressure requirement at the most remote point of the system.

This point is generally established when the hydraulic calculations have been produced for the proposed systems sprinkler system pressure loss due to height combined with the friction losses due to pipe size, pipe length and changes in direction due to the number of fittings used. There will always be an additional 0.5 bar added which equates for the pressure requirement for the last head on the system in order to operate properly.

When pressure losses for the most remote head have been established, this will be documented as the minimum pressure for fire sprinkler system requirement, and this will be always required when carrying out an equivalence test from a pre-determined test point at the start of the system.

How to measure water pressure for sprinklers?

When the minimum water pressure for fire sprinkler system has been calculated and how much water pressure has been established, the existing flow and dynamic water pressure within the town main will need to be established at the system test point positioned close to the point of entry to the property. This is usually done by means of a flow gauge and pressure gauge or can be carried out by running water at the calculated system dynamic pressure into a vessel for a given time duration and then measuring the quantity of water in the vessel.

So, for example, suppose that your fire sprinkler system pressure requirements are 100 litres per minute at 2.5 bar and you have 140 litres per minute flowing from the open end of the incoming supply (this will equate to 140 litres at atmospheric pressure or 0 bar) how to measure water pressure for sprinklers at the system requirement:

1st step: install a ¼ way lever valve,

2nd step: install a pressure gauge upstream of the lever valve,

3rd step: run the supply with the lever valve fully open then close the valve until the required pressure is showing on the pressure gauge behind the valve (in this case 2.5 bar)

4th step: maintain the flow, then divert into the vessel for 10 seconds (say) then multiply by 6.

If you measure 17 litres, then you have achieved your sprinkler system minimum requirement (i.e. 6×17 = 102 litres at 2.5 bar.

Please note that there are other factors that dictate the flow quantity like for example, shared domestic/sprinkler supplies, operation of a priority demand valve, relative position of the domestic take-off to the sprinkler take-off etc.

For more help and advice, find more on our dedicated blog, and if you’re considering installing a fire sprinkler system, or just need some honest advice, one of our engineers will be happy to take your call or inquiry via our contact page.

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Mist system was a great solution for our renovation needs and them team at RAD have been great. Always communicated clearly and been on hand to discuss over the phone as needed. Would highly recommend!
09:32 17 Jul 22
I have used RAD for a couple of projects and found them to be good to deal with. They did a pair of 3 storey open plan houses and seven three and four story town houses. The sprinklers were to improve fire safety, allow more flexible space and comply with building regulations. The sprinklers were far more cost effective than the mist type systems and look very discrete when installed.
Paul Jeary
15:50 11 Jul 22
It has been a pleasure to deal with RAD for installation of fire sprinklers at our site is Sevenoaks. They were fast, professional, working to time and quote, which made it easy to work with them.
Katrina Horobin
12:03 29 Jun 22
My requirement was a bit unusual for RAD in that I wanted a mist system in one room of a rented house. I had no drawings or technical back up. RAD were very helpful and repositioned the unit after the initial installation. Luckily with the help of Sonny, the engineer it all worked out very well.
Simon Gurney
16:16 12 May 22
I have used RAD for the last 10 years for all of my housing developments in need of a sprinkler system. Easy process from start to finish and no issues or problems throughout. Always someone at hand to answer a querie and we have a great working relationship with the team at RAD. Would highly recommend.
15:33 12 May 22
Diligent & a very professional team. A joy to deal with. Will certainly be calling on them to help with many more future schemes.
Jason Tema
22:17 08 Jul 19
Great team, fitting sprinklers, saving lives & property... What more could you wish for!!!
Colin P
17:53 01 Jul 17
Excellent company & great service... This company rocks! They sprinkle fires & save lives!!!
Music N Videoz
07:15 16 Dec 16
As somebody who feels that it should be a necessity for all properties to have fire sprinkler systems, I am a big fan of this company. I have used them numerous times to service my home system and they are very knowledgeable. I would highly recommend their service.
Kate Fraser
09:25 30 Mar 15
One look at Rad Fire Sprinkler's website will tell you that these guys know exactly what they are talking about when it comes to Fire Sprinklers and the legislation surrounding fire safety. A very trustworthy company.
Adam Hudson
16:45 15 Nov 13

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