How Does a Dry Pipe Sprinkler System Work?

Fire protection is extremely important in all types of buildings, considering the potential consequences of uncontrolled fire and smoke. Automatic sprinkler systems are among the best measures you can deploy to ensure occupant safety and to protect property.

Based on their configuration, fire sprinkler systems can be classified into four main types, and the best option depends on the specific conditions in each project:

• Wet pipe systems
• Dry pipe systems
• Deluge systems
• Pre-action systems

This article will focus on dry pipe sprinkler systems, including their applications, advantages and disadvantages.

How Does a Dry Pipe Sprinkler System Work?

According to the NFPA 13 standard, a dry pipe sprinkler system is one that uses automatic sprinklers connected to a piping network with pressurized air or nitrogen instead of water. Pressure holds back water thanks to a dry pipe valve, which is a special type of valve designed for this application. The pressure is released when one of the sprinkler heads activates, opening the dry pipe valve and allowing water into the sprinkler piping. For comparison, a wet-pipe system is permanently filled with water, which is released as soon as one sprinkler head opens.

Operating Procedure of a Dry Pipe Valve

Dry pipe valves are installed at the end of the fire sprinkler riser, separating the pressurized piping network from the water supply.

• As explained above, these valves are held back by a pressure difference - the sprinkler piping generally has a pressure 5 times higher than the water supply to hold the valve closed. A typical system side pressure is 40 psi.
• In some dry pipe valve models, there is a small amount of priming water to achieve a better seal.
• There is an intermediate chamber with a water flow switch and an alarm port, which can be connected to a water motor gong outside the building. Normally, this piping section has no water and is not pressurized.
• NFPA standards require pressure-type flow switches in dry pipe sprinkler systems. Vane-type switches are not allowed, since the water flow is very strong when the valve opens and it can damage the paddles of vane-type switches.

The sprinkler system pressure must be reduced to 6 psi to open the dry pipe valve, but there is a low pressure switch that sends an alarm if pressure drops 10 psi below the nominal value. When this switch activates, it does not necessarily mean that a sprinkler head has opened

• the drop can be caused by issues such as leaks and compressor failure, and the system should be inspected to fix the issue before the dry pipe valve opens. The NFPA 72 standard requires air pressure to be monitored, in order to detect a change of 10 psi below normal air pressure.

There are also many accessories available for dry pipe valves, with functions that improve system operation.

• Accelerators help the dry valve operate faster, as implied by their name. They redirect air flow in the sprinkler piping to reduce pressure faster, lowering the opening time of the valve. In other words, they reduce the time required to deliver water to the affected area after a sprinkler head opens.
• Air maintenance devices keep adequate pressure in the sprinkler piping, by supplying more air when a small pressure loss is detected.
• Air dryers remove moisture inside the sprinkler piping, as implied by their name.

With a background in journalism and a passion for storytelling, Jane has penned multiple bestsellers that have enthralled readers worldwide. Follow on https://www.ny-engineers.com