Cold Water Booster Sets

Overview and Sizing Guide



Water pressure is the force that drives the water through the water fitting (pipe), which is measured in bar. 1 bar equates to 10m in height.
– Water pressure can vary throughout the day; typically it will be lowest in the morning before people go to work and as they come home from work, and will be highest overnight. Static pressure refers to the pressure in a water pipe with all fittings closed, dynamic pressure is pressure recorded as the water flows through the pipework and will vary depending on the size of the orifice that is open. (We would see a drop in static pressure as a tap is opened)

Water flow refers to the amount of water coming out of a hose or a water fitting, and is measured in Litres/sec.

Velocity of water is the speed that water moves through a pipe fitting, measured in Meters/sec.
When we put our finger over the end of a hose to create a jet, we are not changing the water pressure, we are just increasing the speed of the water.

Pipe friction (material), joints, valves, diameter of pipes can all add up to reduced performance as the water travels through a building. If mains water pressure is unable to overcome these restrictions, we will notice a reduced flow from taps and showers. Combination boilers and other specific equipment that require a set pressure will go into fault mode.

A typical kitchen tap is 0.13 Litre/sec. Depending on the restrictions set about above, it will need “X” amount of pressure to drive the water through the fitting at this flow rate.

To overcome these restrictions, we fit a cold-water booster set on the incoming main, which increases the pressure and the flow rate. The 1999 water regulations allow us to fit a pump directly to the mains supply as long as it does not exceed 12 litres/min (0.2 Litres/sec) as anything greater than this has the potential to draw the water from the mains supply and surrounding properties.
While this is sufficient for a shower, it will not cover a whole house problem.
For larger flow-rates we must fit a break tank between the mains supply and the booster set, as this will remove the potential for the pump to suck the mains supply dry.

Traditionally break tanks are quite large and filled slowly via a float valve, the connected pump would draw the water from the tank and boost around the house. Besides taking up space, we have the risk of stored water arming up and promoting bacterial growth.

Arrow Valves “Pent-A-Boost” units combine the break tank and booster pump in one small unique package. The break tank is fed by a full-bore solenoid valve(s) which, unlike a restrictive float valve does not hamper the flow through its body. Because we have lost these restrictions, the break tank can be down sized considerably. Our break tanks are 24 litres, if the pipework feeding the tank is the recommended size and a statutory 1 bar is provided the tanks will stay flooded, and the pump(s) will boost accordingly.


Sizing pumps can vary between properties – important factors being the height of the building  (bar) and the fittings within the building. 3 bar at any appliance is more than sufficient in most situations, typically a 3-4 bedroom properties require 1.0 litre/sec at 3 bar and 4-6 bedrooms 2.0 litre/sec at 3 bar. We have a unit capable of 3.5 litres/sec @ 3 bar for larger properties.

Diversity plays an important factor when sizing pump sets, as if we were to add up all of the fittings within a house the loading would be significantly higher than we actually require. We would never have a situation where baths, showers, washing machines, WC’s outside taps were all running at once. There are loading guides and equations to predict the exact requirement. (Institute of Plumbing. (2002) Plumbing Engineering Services Design Guide.) One source of said information.

High efficiency variable speed motor drives allow quite operation and consume less energy than their equivalent fixed speed pump versions.

The table below shows depicts various flow rates and pressures, and the pumps that will attain this duty.


Post Lockdown Pump Maintenance Checklist

Checks to your units are in working order



As the UK’s lockdown is being gradually eased after almost ten weeks, a number of pump sets on commercial sites would have sat idle for this period of time. Once it is safe for us to resume working, there are three key checks we can perform to ensure that our units are working correctly, and prevent pump damage, potential flooding and using stagnant water.


– Check 1 – Seized Pump

If the pump has not been used for several weeks, there is a strong chance that it could be seized. The symptoms for this are a hot pump making a humming noise, and no water being delivered by the unit. If the pump is seized, the fan will need to be rotated to free the pump.


– Check 2 – Filling Mechanisms

It is important that the filling mechanism on our tanks, whether that is a solenoid or float valve, are switching on and shutting off correctly. A constantly filling device will result in the tank overflowing and a potential flood risk. If the device won’t shut off, it should be removed and cleaned.


– Check 3 – Stagnant Water

During the lockdown, which has had predominantly warm weather, water would have been sat unused in tanks and connecting pipework. This water could be a Legionella risk and unsafe to use. It is important to ensure tanks are clean and any stagnant water is flushed from the system before use.


Please contact us if you require any further information on the checklist, or if you would like us to attend site and perform the checks for you.



What we’re doing

An update from Arrow Valves


An update from Arrow Valves…

We wanted to take the time to get in touch to let you know what’s been going on at Arrow Valves during these unprecedented times.

Firstly – we remain open to support our customers who need us. Our stock levels are good, and if you have an urgent order, we will do our best to get this delivered to you as quick as possible.

Whilst our office staff are now working from home – we remain available on the other end of the phone for project guidance, and quotations.

During this difficult time, we are taking steps to work on communication continuity – and this involves filming our Water Regulations seminar. This will allow our clients to continue their education and CPD accreditation while working from home.

In the meantime – all our Water Regulations tutorials remain free to download from our website here.

We understand the challenges everyone is facing, and we send our best wishes to all of you. If we can do anything for you – please call us on 01442 823123.


Expansion Vessel Sizing Guide

Start here for help with vessel sizing


Sealed Heating Systems need to be designed so that we control the maximum temperature that the system reaches and have adequate management in place, should this maximum be exceeded.

Within these systems, the thermal expansion of water must be compensated for and this is normally achieved with an expansion vessel.

Vessels are sized according to the volume of the system, the maximum temperature that the system generates, and also the head above the vessel.


Arrow Valves manufacture a range of pressurisation units and expansion vessels – we can provide these as a complete package with all required ancillaries and the correct vessel sizing.

We can also provide assistance with vessel sizing for specifiers – click here to view our expansion vessel guide or contact us with your system parameters.

Click here to view our expansion vessels & pressurisation units.




Safe Hot Water – Fluid Category 5

Does your system design comply with the water regulations?


There are times when we need to deliver hot water at a safe temperature, but also ensure that we manage the RISK OF CONTAMINATION to mains water with an appropriate backflow prevention device.

Examples include:

  • Toileting facilities – the use of bidet hoses that can be submerged in the WC pan
  • Showers in care facilities where the shower head can be submerged in the bath, and
  • Showers that are used in pet grooming

All these scenarios require blended warm water but also pose a fluid category 5 risk, so we need to introduce a suitable air gap, via a break tank.

Storing hot water in this break tank becomes a problem –

  • As this water cools down, it becomes a breeding ground for bacteria and introduces the risk of legionella.
  • Water would be wasted, as the tank would need to be purged of the cold water before hot water is useable.
  • We introduce the risk of scalding, particularly with vulnerable end users in care homes, and so it is imperative that water is delivered at a safe temperature.

There are a few solutions to combat these problems –

  • We can feed a CAT 5 unit with blended warm water – such as the AB2 shower break tank, or hot water midi unit.
  • We can have a unit that is complete with all the necessary equipment for backflow. protection, heating water and regulating the temperature, such as the Ablution Unit.
  • We can feed an electric shower with a cold-water CAT 5 unit – such as the Care Shower package.

There are problems associated with hot water, but these can all be overcome with clever and innovative products. This ensures we are compliant with Water Regulations in not allowing contamination of the mains supply, but also able to provide water at safe temperatures to our end users.


Link to Hope & Arrow Valves

Shoebox Charity appeal – December 2019


Arrow Valves team members compiled shoe boxes during December 2019 for donation to less fortunate families and elderly in Romania, Bulgaria, Moldova and Ukraine at Christmas.  More information can be found on the Link to Hope blog.

Click here

Link to Hope support vulnerable families in Eastern Europe in the areas of education and social care; working towards safe living environments, healthcare, human rights, employment and education.


Protect your lab taps

Improved DC Pipe Interrupter: For use with laboratory taps


Our model DC15F257 Pipe Interrupter was specifically designed to be installed on the outlet of a laboratory tap that has the removable nozzle taken off, providing the highest level of protection against back siphonage, as required under the Water Regulations.

This model now has an integral clutch mechanism, which locks the device in place once fully screwed on. This makes it much more secure and prevents any chance of it from being removed after installation – ensuring the Fluid Category 5 protection is always in place.

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December 2019

Donation to “The TOY Project”


Sustainability is very important to the Arrow Valves

For Christmas this year, we’ve sent e-cards instead of traditional paper cards, and have donated £1,000 to ‘The TOY Project’ instead.

‘The Toy Project’ helps children deal with their grief through play – providing toys for use by organisations involved with child bereavement.

Each year in the UK over 20,000 children under the age of 18 experience the death of their mother or father– around 60 young people bereaved of a parent every day.

We know that ‘The Toy Project’ will put our donation to good use. This charitable organization provides toys for children in hospitals and hospices, children in refuge centers, and they provide toys for schools and nurseries and to vulnerable families.

For more info please head over to