Learn About an OS&Y Valve for Fire Sprinkler Systems and Water Mains – A Great Guide

An OS&Y valve is the type of valve required by code for NYC water main service lines that provide fire protection. When installing a new water main for fire protection it is vitally important to use the correct main control valve inside the building. 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.

The importance of an OS&Y valve goes much farther than that though. An OS&Y valve provides unique protection that a typical gate valve or ball type valve cannot provide. Watch our main control valve video that follows for a greater understanding of the various types of water valves. The correct and code complaint valve is required regardless of the size of the water service line or the material the water line is made of.

What is an OS&Y valve on a water line?

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 an OS&Y valve actually raises and lowers visibly outside the body of the valve. On the other hand, the handle itself 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. 

How do you know when an OS&Y valve is open or closed?

With an OS&Y valve it is always clear whether the valve is open or closed. This is vitally important for properly maintaining fire protection. Read a more technical explanation from Mueller, a manufacturer of valves. Knowing conclusively that a valve is opened or closed also greatly helps avoid damaging the valve by over tightening it.

The fact that it is always perfectly clear whether an OS and Y valve is open or closed seems to add to it’s longevity. The stem being visible, clearly being either raised or lowered, takes much of the guesswork out of operating the valve. Therefore, excessive force is less likely to be used in operating the valve.

Because OS&Y valves are UL rated, they seem to be better constructed than many other typical water valves. They are likewise a bit more expensive than a typical water 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. That is why an OS&Y valve is required on any existing fire service main or when any water service main replacement is needed which provides fire protection.

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.

Why are OS&Y valves locked?

On NYC water main installations for fire protection all main control valves must be locked in the open position. This avoids someone accidentally closing the valve and deactivating the fire sprinkler system for the property.

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 (UL stands for Underwriter Laboratories, which is a global independent science company).
• Must be locked in the open position to ensure fire protection is active.
• Must be the same size as the water service line. The valve size cannot be either larger or smaller than the service line size.

What to do if an OS&Y valve leaks or the handle will not move

On every OS&Y valve there is a packing nut, or packing screws. The purpose of these is to hold the packing material of the valve tightly in place so there are no leaks. Sometimes the packing nuts can be too tight or too loose.

If the valve handle on an OS&Y valve will not move, the packing may be too tight. Do not use brute force to make the handle move. Simply loosen the packing nut or packing screws a couple of turns. The handle should then move freely. Afterwards remember to tighten pack the packing.

Frequently if a leak appears on an OS&Y valve it is because the packing is too loose. Simply tightening the packing nuts of screws will stop the leak. This can be easily accomplished using any common wrench, and does not require a skilled plumber.

Never cut corners by installing an inferior or non-code complaint water valve

Never cut corners when it involves fire protection for your family or your property. Ensure that your plumbing contractor doesn’t either. The more you know the safer you, your family, and your property may be.

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.

Fire sprinkler heads activate on an individual basis

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.

How does a fire sprinkler head activate?

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.

Some closing words about an OS&Y valve

It important to reiterate, when water supply is for fire protection, never cut corners, take a short cut, or skimp on material. That is regardless of if your your fire protection system involves a Siamese connection or not. With that having been said, always utilize an OS&Y valve where required by plumbing or building department code. This type of valve is more expensive than a typical gate valve or ball valve, but that fact should be a distant second factor to the safety of a building’s inhabitants.

The NYC Water service line and fire service line expert

If you reside or are a property owner in NYC, Balkan Sewer And Water Main is the largest and most trusted service for over 70 years. No matter the nature or need, if it involves plumbing and it underground, Balkan is The Team You Trust. Fele free to contact us for expert advise, or receive a rapid quote using our expedited online quoting process.