Cyclical Fill and Vent Purging Options

for Gas Pressurized Sprinkler Systems


In order to get the most benefit from using 99% nitrogen as the pressurizing medium for gas pressurized sprinkler systems, it is important to remove the air that is already in the piping at the outset, especially if the initial pressurizing uses compressed air to meet the 30 minute NFPA rule.  Holtec has developed and patented a technique to effectively accomplish this in the period following switching on of the nitrogen supply.  This method involves repeated cycles comprising a small increase in pressure (3 to 5 psig) by feeding nitrogen gas into the system followed by an equal reduction in pressure by venting gas from the system. Each “fill and vent” cycle, akin to breathing, takes several hours to complete and multiple repeated cycles over a period of about 30 days are required.  A more detailed description of this process which compares this superior engineered approach to purging under static pressure conditions is available upon request to Holtec. Note that Holtec’s patented fill and vent purging conveniently allows the vent to be located right at the riser and not at some remote location at the end of a header.


Holtec offers four possible options for achieving this type of purging, as summarized below:


The HCV-M manual vent is installed in the sprinkler piping and is the simplest and least expensive option.  The manual inlet valve is opened by a technician when the zone is first pressurized and then manually closed after 15 to 30 Days.  The pressure cycling to create “breathing” is controlled by the Holtec nitrogen generator.  This vent is automatic in the sense that venting will cease if the pressure in the zone falls below a value pre-set on the built-in  back-pressure regulator. (See Link below)


The HCV-T timed vent has all the features and functionality of the HCV-M vent but, in addition, includes a solenoid valve.  This valve is powered “open” and closes automatically after a pre-set time period of 15 to 30 days.  The controlled timing feature comes from individual wall-mounted enclosures, one for each vent, and each requires a 120V power supply.  For multiple risers in close proximity, the control timing can be from a single controller powered from a single 120V power supply.

This time-controlled option means that there is no need to remember to revisit the site and/or climb ladders, etc. to manually close the vents.  (See Link below)


The “SMART Manifold” is Holtec’s most automated and technically advanced option for fill and vent breathing and maximizes the efficient use of the nitrogen. The cyclical fill and vent process is precisely controlled independently for each zone by solenoid valves responding to pressure signals through a PLC.  The venting process of each zone is independently halted after a pre-set number of breathing cycles has been completed for each zone.  Again, the total time taken is typically 15 to 30 days, but will vary for each zone.   Manifolds are wall or rack mounted and are supplied in versions designed to serve from 2 to 10 zones (N designation).  Venting is internal to the manifold without the need for vents to be installed on the actual sprinkler piping. Below are pictures of a 2-zone and 5-zone SMART Manifold. Note that an air maintenance device is built-in for each zone.

Holtec has developed a fourth method which will be available soon for single zone systems or for multiple systems where the risers are widely spaced.

With both of the above "SMART" devices, the PLC controlling the process can be customized to provide electronic signals to a Building Management System (BMS) such as low pressures or short cycles which would indicate excessive and unacceptable leakage rates from the individual zones.

Each Manifold requires a single 120V power supply, as will our new proprietary method.

2-Zone SMART Manifold, Expandable to 4-Zone

Download the HCV-T Product Spec Sheet

Download the HCSM Product Spec Sheet

Contact Us

18167 Edison Avenue, Unit I, Chesterfield, MO 63005

Phone: 1-636-532-6613 • Fax: 1-636-536-7863

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