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Pressure reducing valves: does size matter?

  • 17 April 2020

The most efficient and cheapest medium for fighting fires is water. Every fire service uses water in one form or another in their battle against fires and Pressure Reducing Valves are an indispensable part of any wet firefighting protection system.

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There may well be instances where the normal firewater mains pressure may exceed the safe operating pressure of the portable firefighting equipment, in which case a PRV will eradicate this potential risk. A PRV will reduce the pressure of firefighting water from a fire main to a lower pressure suitable to supply hand-held nozzles via flexible firehose.

Once the valve is set to the desired downstream pressure, this reduced pressure will be maintained regardless of changes in the supply pressure and any system load variations. PRV valves can be supplied in a wide range of threaded or flanged inlet styles with various outlet adaptors to ensure compatibility with existing equipment.

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Prv’s and fm certification

In October 2017 FM approvals introduced a new requirement for Low Pressure Friction Loss Testing to PRV’s in accordance with section 4.11 of FM 1521 / 1522 to the Approval Standard for Pressure Reducing Valves FM1362. To achieve approval “The measured friction loss shall be less than 10 psi” (This test is performed in a condition where the inlet pressure is below the set outlet pressure of the valve).

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The result of this new requirement was that when applied to the 2 1/2” (DN65) size valves all manufacturers were de-listed from the FM approvals guide and the scramble was on to find an acceptable solution.

Specifications in industrial firefighting state valves should be approved (preferably FM or LPCB) and be capable of flow rates up to 946 l/min (250 GPM) or even up to 1135 l/min (300 GPM) depending on each customer’s specific application.


The Knowsley response was to take the toughest route and obtain approval of our 2 1/2” (DN65) valves. This was due to the high flow rate requirement and the need to ensure that the fluid velocity through the valve was at limits we considered acceptable.

Were other solutions possible? A simpler route to reduce the valve outlet size and obtain approval with a reduced bore size of 1 1/2” (DN 40) was possible but in our evaluation, we considered the total operating range of the valve; and the resultant high water velocity at operational flowrates which at 946 l/min would be approximately 14m/s (50 km/h) through a 1 1/2” bore.

For Knowsley SK Ltd only 2 1/2” bore size was acceptable where velocity would be below 6m/s which is the goal in firefighting systems.

We are proud to confirm that we maintain FM Approval for the Hosesafe PRV at 2 1/2” DN65

PRV’s are also covered under BS5041-1:1987: Fire hydrant systems equipment – Specification for landing valves and wet risers.  This states a minimum water flow rate through the valve of no less than 8.5L/s (510 l/min) and an outlet pressure of no less than 4 bar when the inlet pressure is 4.7 bar

We are proud to confirm that we maintain BRE LPCB Approval for the Hosesafe PRV at 2 1/2” DN65
At Knowsley SK, fire safety and the protection of people, assets and the environment are our number one priority and we will never compromise on those values.

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Hosesafe ii (3100 series)

The re-designed HoseSafe II Pressure Reducing Valve range is based on the Series 1400 Landing Valve which was first brought to market in the 1990’s and is a well-established and well-respected product within the fire safety community. The HoseSafe II can be used on fire mains with a working pressure as high as 20 barg, whereas the outlet pressure can be adjusted to client requirements anywhere between 3 to 8 barg.

Used primarily in the Oil & Gas, petrochemical, chemical and in wet rising mains in buildings the HoseSafe II can be used with fresh, brackish or sea water, making it extremely versatile.  The re-designed PRV eradicates any issues that may arise from water freezing within the PRV making it suitable for use in lower temperature climates.

Available in various configurations including bibnose, oblique and horizontal and with 2 ½”threaded or 3” or 4” flanged inlet types the HoseSafe II series is FM Approved and BRE Global LPCB approved to BS5041-1 and achieve a flow rate of 946lpm (250gpm)

To download the product datasheet please click here

To discuss your application with one of our customer service team please email [email protected] or call +44 (0)161 872 7511

For more information on FM approvals click here. For information on LPCB click here

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