Let’s Talk Pressure Regulating
There is a lot of confusion out there when we talk about pressure regulating devices, especially when referring specifically to fire department hose connections on standpipes. The confusion lies somewhere between the standards and how we refer to the specific devices. The 2019 NFPA 14 Standard for the Installation of Standpipes and Hose Connections has clearly defined not only what a pressure regulating device is but went a step further in defining both pressure regulating valves and pressure restricting devices. This is a key in understanding the operational differences between the design applications.
First, we must be clear in understanding the basic difference between the term static and residual pressure as it relates to water. Static water pressure is simply the pressure of water when not flowing or motionless. Residual water pressure, on the other hand, is the pressure of water when flowing or working pressure, used in early code terminology. This basic understanding will allow us to better understand what we are regulating, and which devices are required.
Pressure regulating devices (NFPA 14, Section 3.3.16) are designed for the purpose of reducing, regulating, controlling or restricting water pressure. When a pressure regulating device is installed as part of a hose valve, it is either a pressure reducing valve (NFPA 14, Section 184.108.40.206) or pressure restricting device (NFPA 14, section 220.127.116.11). The pressure reducing valve (PRV) is designed to reduce both residual (flowing) and static (non-flowing) water pressure. While pressure restricting devices (PRD’s) are designed to only control residual (flowing) water pressure.
This differentiation is vital to understanding the design application and expectations of the system. The current edition of NFPA 14 requires the following:
All class I & III standpipe systems to flow a minimum of 500gpm though the two most remote 2½” hose connections, NFPA 14, Section 18.104.22.168.1.
States you must provide a minimum residual design pressure of 100 psi at that most remote hose connection, NFPA 14, Section 7.8.1.
Where pressures exceed 175psi, a listed pressure regulating device shall be provided to limit both static and residual pressures, NFPA 14, Section 22.214.171.124.3.
By definition, the only pressure regulating device capable of regulating both static and residual pressure is a pressure reducing valve (PRV).
It must be noted than when hose connections are above the maximum allowed, they may be restricted or reduced to any pressure within the acceptable range within the two design limitation criteria of pre-1993 (100psi) vs post 1993 (175psi). This pressure can also be factory set or field adjustable at the hose connection. This is significant as field adjustable set pressures may be able to be increased with specific tools and knowledge, while factory set cannot.
This leads us to the discussion of the design application for pressure restricting devices. PRD’s where typically used in earlier designs editions of NFPA 14, prior to the 1996 standard that increased the minimum from 65psi minimum/100psi maximum, to the current standard of 100psi minimum/175psi maximum. The pre 1996 standard required outlet pressures that exceeded 100psi to be reduced with an approved device. The device was only required to restrict residual (flowing) water pressure making PRD’s and common choice in the design of the day. This design justification was based on fire department hose/nozzle packages dating back to the 1950 and had not yet been adjust until the 1996 editions of NFPA 14 was released.
In the 2017 NFPA 25 Standard for the Inspection, Testing, and Maintenance of Water-based Fire Protection Systems, in Chapter 13, Common Components and Valves, the requirements for Pressure reducing valves (PRV), requires them to be fully flow tested every five years (NFPA 25, Section13.5). The confusion falls in Section 13.5.2 governing testing requirements for Hose Connection Pressure Regulating Devices. The section is trying to reference pressure restricting devices but uses the umbrella term of regulating. This continues in 13.5.3 with requirements for hose rack assembly pressure regulating devices, once again using regulating instead of restricting. Although the misuse of “regulating” devices unintentionally still covers the required maintenance for all devices designed for the purpose of reducing, regulating, controlling or restricting water pressure, it should be addressed by the NFPA 25 committee.
2018 NFPA 1 Fire Code (NFPA 1, Section 126.96.36.199.2) states that hose connections shall be in accordance with NFPA 13, unless class II or Class III standpipes in accordance with NFPA 14 are used. This is an extract from 2015 NFPA 101 Life Safety Code (NFPA 101, Sections 188.8.131.52.2 and 184.108.40.206.2) and was extracted from the assembly chapters of that document. This section applies to stages but was extracted to NFPA 1 Fire Protection Systems standpipe system chapter leading to confusion of the standard governing requirements for hose connections. This section has been removed in the 2018 edition of NFPA 101.
NFPA 13 Standard for the Installation of Sprinkler Systems, does address maximum pressure for 1½” hose connections (NFPA 13 – 220.127.116.11.4 (6)). NFPA 13 also allows 2 ½” hose connections for “Fire Department Use”, to be added to sprinkler only designed systems (NFPA 13 – 18.104.22.168) but does not address any pressure provisions for 2 ½” hose connections. The disconnect is fire department use implying that the hose connection meets the requirements for structural firefighting. The * following section 22.214.171.124.2* indicates that an annex note in reference to this issue exist and states the flowing.
Hose connections of 2 ½” are permitted to be attached to wet pipe sprinkler systems only. These connections can be used for final extinguishment of the fire or to cool residual heat. These connections are also not to be treated as standpipe hose connections. If standpipes are installed and the standpipe risers also supply the sprinklers, all provisions of NFPA 14, including waters supply and pressure provisions, need to be followed. When either one of the hose connections described in 8.17.5 is provided, the flow rates need only be added to the sprinkler system at the design pressure available at the point of the connection to the sprinkler system pipe.
NFPA 13 clearly allows the use of a 2 ½” hose connection on a sprinkler system only design but that hose connection is not required to meet the fire service pressure provision and should not be consider for structural firefighting only mop-up.
Understanding the design difference between the umbrella term of pressure regulating which covers all things that reducing, regulating, controlling or restricting water pressure and the more specifically defined terms of restricting and reducing that delineate residual (flowing) and static (non-flowing) reductions. It is not only key to proper design and installation of hose connections but imperative to fire service operations. The fire service must understand the implications of the design criteria used in the installation of fire protection systems in buildings and the limitations of the system design.