What is Valve Seat Leakage?
Like any part of your machinery, the valve seat can undergo wear and tear over time, which affects its functionality. One of the most common valve seat problems is leakage (which can occur even when your valve is off). If left unaddressed, excessive valve seat leakage can interfere with production and can ultimately lead to unplanned downtime.
The ANSI FCI 70-2 offers six different classifications for valve seat leakage, which will tell you the following:
- The maximum amount of leakage permitted
- Medium used to test valve
- Pressure used to test valve (in pounds per square, or psig)
Let’s take a more in-depth look at each of these classifications.
Class I (Dust Tight)
The first class is for metal or resilient seated valves. While it has the same design and construction as classes II, III and IV, it does not come with a maximum leakage amount or any testing procedures.
Class II
This class is designed for double port or balanced single port valves (generally with a metal piston ring seal and metal to metal seats).
- Maximum leakage allowed: 0.5% of rated capacity
- Test medium: Air or water at 50-125⁰ F
- Test pressure: 45-60 psig
Class III
Like Class II, this class is made for double port or balanced singe port valves.
- Maximum leakage allowed: 0.1% of rated capacity
- Test medium: Air or water at 50-125⁰ F
- Test pressure: 45-60 psig
Class IV (Metal to Metal)
Class IV is designed for single port and balanced single port valves that have extra tight piston seals and metal to-metal seats.
- Maximum leakage allowed: 0.1% of rated capacity
- Test medium: Air or water at 50-125⁰ F
- Test pressure: 45-60 psig
Class V
Class V is intended for the same valves as Class IV. However, it differs in terms of maximum leakage amount, test medium and test pressure.
- Maximum leakage allowed: 0.0005% of rated capacity
- Test medium: Water at 50-125⁰ F
- Test pressure: Maximum service pressure drop
Class VI (Soft Seat)
This class is reserved for soft seat valves, in which either the seat or shut-off disc (or both) are made of a resilient material, such as Teflon.
- Maximum leakage allowed: 0.15 to 6.75 ml per minute (depending on valve seat size)
- Test medium: Air or nitrogen at 50-125⁰ F
- Test pressure: 50 psig
What Causes Valve Seat Leakage?
Valve seat leakage can be caused by several problems, such as:
- Damage
- Open valve
- Improper sizing
- Improper installation
- Low quality
Over time, your valves may become damaged. Even a small amount of damage inflicted upon the seat or the valve seal can result in leakage. In other cases, the valve may simply not be closed. Anything from dirt to debris can prevent your valve from closing properly.
Alternatively, you might simply have an ill-fitting or low-quality valve. Some valves come with weak off/off capabilities that negatively affect their function, while others are simply not installed correctly.
How Can I Recognize Valve Seat Leakage?
If you’re not sure whether your valve seat is in top-notch condition, it might be a good idea to check. The test used to evaluate valve seats depends on the classification:
- Classes II, III AND IV: Pressure is applied to the valve inlet while the outlet is open.
- Class V: Pressure is applied to the valve inlet after the body cavity and connected piping is filled with water.
- Class VI: The vehicle’s actuator is adjusted based on the operating conditions, while a closing thrust is applied to the valve plug seat.
Depending on the cause of the leakage, you might be able to resolve the problem quickly (for instance, if the valve seat is blocked, the issue can be solved by removing the obstruction). In more severe cases, you might need a replacement. When selecting a replacement, it’s important to go with a high-quality brand that can guarantee durability and longevity, such as Everlasting Valves.
Everlasting Valves: Prevent Leakage Today
The valve you pick can make a huge impact when it comes to stopping leakage and preserving the quality of your machinery. The stronger the valve, the less likely you are to experience problems. This saves time, energy and effort in the long run.
At Everlasting Valve Company, we offer high-quality valves designed to outlast standard, industrial valves. They come with the following features:
- Unique open-body design
- Tight seals that are resistant to leakage
- Self-lapping, rotating disc that clears out process material
While other valves may wear out over time, Everlasting valves continue to strengthen and thrive. Request a quote today to learn more!