A mains fed system means a sprinkler system without a pump and tank – but how do you know that your supply is good enough?
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What is a mains fed sprinkler system?
A mains fed system, also often called a direct feed system, is a sprinkler system which doesn’t need a pump and a tank. This can save substantial cost and space on your development, but systems need to meet certain criteria before they can be certified as being a compliant mains fed system.
How do you know if your mains supply is good enough for a mains fed sprinkler system?
As part of our installation proposals, we always provide detail on what kind of pressure and flow is required for a mains fed system. This guide is intended to support developers in verifying whether or not their property meets that threshold. Ultimately, we would need to confirm the results ourselves before we can certify the installation of a mains fed system, but this guide can prove useful to those who are looking to gain an early understanding of whether or not they need a pump and tank.
We do advise that developers always assume that a pump and tank will be installed until they have had confirmed values from a certified installer. However, local plumbers can often provide reliable results at this stage too.
The most important tests are:
- A pressure and flow test;
- Checking the stop valve;
- Pipe diameter check
Checking your pipe diameter
For domestic properties (houses and bungalows), anything 32mm and above is a solid candidate for a mains fed supply. While this still won’t guarantee its compatibility, anything lower than 32mm is unlikely to be suitable.
This diameter refers to the internal diameter of the pipe at the stop valve.
Check your stop valve
If your stop valve isn’t working, you won’t be able to shut the water off when needed and will need to be replaced. The following video, from Wessex Water, demonstrates how you can check that this valve is working yourself.
What is a pressure and flow test?
A pressure and flow test is the most involved test when assessing whether or not your property is suitable for a mains fed sprinkler system.
A pressure and flow test is a diagnostic assessment used to measure the pressure and flow rate of water through a pipeline, typically within a building’s plumbing system or an external water supply line. For sprinkler systems, this is a process used to verify the quality of the infill into the property from the public supply to confirm whether a mains fed system would be effective. These tests are crucial in construction and building maintenance to ensure that a property has an adequate and reliable water supply for daily use and safety systems, such as fire sprinklers.
Key Aspects of Pressure and Flow Testing
- Water Pressure Measurement: If the water pressure is too low, a mains fed system wouldn’t be able to push water to the furthest sprinkler head. The test measures static pressure, which is the pressure in the water system when no water is flowing, and dynamic or residual pressure, which is the pressure when water is actively flowing. Static pressure provides a baseline measurement, while residual pressure indicates the pressure loss under flow conditions. This helps determine if there is sufficient water pressure for all intended uses within the property. It shouldn’t be assumed that a sprinkler system can be mains fed simply because your boiler doesn’t have a tank. Pumps in modern boilers are now internal. Also, for sprinkler systems, we’re mostly interested in residual pressure, which ensures that the pressure is high enough to spray the water out of the sprinkler at the end of the pipe, not simply reach it and trickle out. It’s the residual pressure which should be measured when testing for a mains fed system. The pressure is measured in bar.
- Flow Rate Measurement: Flow rate is the volume of water that flows through a pipe in a given period, measured in liters per minute (LPM). If the flow rate is too low, not enough water will be in the system to suppress a fire when needed. This measurement shows if the water supply can meet peak demand requirements, such as during simultaneous usage of multiple fixtures or during emergencies.
- Applications: Pressure and flow tests are often required in new construction to verify compliance with building regulations. The process isn’t only useful in assessing mains fed fire protection system installations, but also in regular maintenance to prevent pressure-related issues. For example, if a system has high static pressure but low flow, it may indicate a blockage or undersized piping that could disrupt the domestic supply.
For more information, resources like WRAS and NFPA offer in-depth insights on testing standards and best practices.
How does pressure and flow affect water supplies?
A pressure and flow test should be carried out for all domestic and residential sprinkler and mist systems, to ensure that the infill is fit for purpose, particularly if a mains fed system is preferred.
Pressure can be considered to affect how far along the pipes water can be pushed. Whereas flow can be thought of as the amount of water which is flowing through the pipe. Domestic water doesn’t have the same requirements for pressure and flow as mains fed sprinklers, so mains fed sprinklers need their own checks.
If there isn’t enough pressure, we need something to push the water further, which is why we install a pump. If there’s plenty of flow but not enough pressure, we can install a pump without a tank.
If there isn’t a high enough flow, the empty space in the pipe fills with air, which isn’t useful for putting out fires. Even worse, bubbles in pipes can cause airlocks which can prevent the system from working at all. If there isn’t enough flow, we need to put more water in the system by installing a tank. If there’s not enough flow, we need something to help us move the water out of the tank. Even if there’s enough pressure at the infill, we still need a pump in order for the tank to be useful.
Who should take a pressure and flow test?
Ultimately, the measurements need to be verified by the installer, but we encourage clients to carry out their own tests during the pre-tender stage to ensure impartiality. This preliminary test doesn’t need to be carried out by a specialist sprinkler installer and can be carried out by a plumber.
As part of our sprinkler and mist proposals, we detail the infill which we would require in order to for the system to be compliant. For dwellings, these figures are usually the pressure and flow required for a direct mains feed (so a system which would require neither a pump or a tank). These figures do not need to be verified by a sprinkler installer at this stage and so we encourage prospective clients to reach out to a local plumber to confirm the values.
This approach benefits from impartiality. You know for a fact that the values which your plumber provides are honest and accurate. Sprinkler and mist installers who verify the infill before confirming the water supplies have a vested interest in providing the most pessimistic figures in order to secure an order for water supplies. We don’t want to sell anybody something which they don’t need. If, within your pre-tender information, you are able to meet the infill requirements detailed in our proposal, we will gladly provide you with a direct feed. Clients are, however, asked to note that we do verify the infill of all installations prior to commissioning.
This approach also benefits from being able to leverage contractors who may already be on site. New builds may already have a plumber on site for the central heating installation, while larger retrofit developments may have onsite personnel who are able to provide the measurements needed.
What do the regulations say?
Sprinkler systems in dwellings in the UK are regulated by BS 9251: 2021, which require work to be carried out by competent professionals. This is why we always verify any measurements sent to us by clients.
The standard also details the equipment to be used for the test itself, as shown in the image below.
What equipment should be used?
Proper equipment ensures accurate measurements. As firas accredited installers, we’re required to use the following equipment.
Pressure measurement
A pressure gauge, which has been calibrated within the last 12 months, and is filled with glycerin for a more stable readout. Suitable models are available from Sale Engineering.
Measuring flow
Flow should be tested using a specialist device, such as an F-1000 flow meter, available from Rapidrop. If you don’t have access to a flow meter, a rough approximation can be calculated by recording how long it takes to fill a bucket. So, if it takes 15 seconds to fill a 15 litre bucket, you’re running on around 60 litres per minute.
The test should be taken from just downstream of the stop tap, rather than at your kitchen sink. The difference in pipe sizes will affect the results.
How to take a pressure and flow test
A typical test will follow the steps below. The test should be taken during a period of peak demand for the local area (typically between 5pm and 7pm):
- Connect the test rig to the system test and drain valve.
- Connect a sufficient length of drain hose of at least equal internal bore to the end of the test rig, with the open end run to a suitable surface drain or receptacle. Ensure that the hose is as straight and level as practicably possible to minimize frictional losses. Do not submerge the open end of the drainpipe.
- Close the stop valve (see Figure E.1) and slightly open the test and drain valve until pressure stabilizes in the flow test assembly, then fully open the test and drain valve.
- Slowly open the stop valve until the design requirement flow is registered on the flow meter OR the design requirement pressure is registered on the calibrated pressure gauge.
- Take readings from the flow meter and calibrated pressure gauge and check that they both meet or exceed the design requirements of the system. If so, the water supply is deemed to be adequate.
- The test should be repeated for each design requirement.
In practice, it is often prudent to take measurements by opening the tap to 25%, 50%, 75%, and 100% to produce a curve for the design process. We always verify the results prior to commissioning in any case.
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