When installing a new water main for fire protection it is vitally important to use the correct main control valve inside the building. An OS&Y valve is the type of valve required by code for NYC water main service lines that provide fire protection. Even on a water main repair of an existing line for fire protection the main control valve should be checked that it is code compliant. But it goes much farther than that – an OS&Y valve provides unique protection that a typical gate valve or ball type valve cannot provide.
What is an OS&Y valve?
Technically OS&Y stands for ‘outside screw and yoke‘ That means that when the handle is turned it directly raises and lowers the gate of the valve by interacting directly with the stem of the valve. The handle and the stem are both threaded so they interact together. The stem of the valve itself raises and lowers visibly outside the body of the valve, while the handle remains in a fixed position. As the stem rises the gate inside the body of the valve rises in unison letting water flow through the body of the valve.
Why is an OS&Y valve so important?
Because a fire sprinkler main is dedicated for fire protection and not for any domestic use, you cannot test in the usual fashion if the water is on or not. In other words flushing a toilet or turning on a sink will not let you know if the fire sprinkler system is active. One quick look at an OS&Y valve with the stem raised out of the body of the valve and you will know that the water is on. On a typical gate type valve a visual inspection cannot determine whether the valve is open or closed.
The NYC plumbing code and OS&Y valves
- All main control valves for fire protection must be ‘Outer Stem & Yoke’ type valves.
- All valves must be UL Listed.
- Must be locked in the open position to ensure fire protection is active.
- Must be the same size as the water service line – It cannot be reduced in size.
How does a fire sprinkler head operate?
courtesy of wikipedia
Each closed-head sprinkler is held closed by either a heat-sensitive glass bulb or a two-part metal link held together with fusible alloy such as Wood’s metaland other alloys with similar compositions. The glass bulb or link applies pressure to a pip cap which acts as a plug which prevents water from flowing until the ambient temperature around the sprinkler reaches the design activation temperature of the individual sprinkler. Because each sprinkler activates independently when the predetermined heat level is reached, the number of sprinklers that operate is limited to only those near the fire, thereby maximizing the available water pressure over the point of fire origin.
The bulb breaks as a result of the thermal expansion of the liquid inside the bulb. The time it takes before a bulb breaks is dependent on the temperature. Below the design temperature, it does not break, and above the design temperature, it takes less time for higher temperatures. The response time is expressed as a response time index (RTI), which typically has values between 35 and 250, where a low value indicates a fast response. Under standard testing procedures (135 °C air at a velocity of 2.5 m/s), a 68 °C sprinkler bulb will break within 7 to 33 seconds, depending on the RTI. The RTI can also be specified in imperial units, where 1 ft is equivalent to 0.55. The sensitivity of a sprinkler can be negatively affected if the thermal element has been painted.