1. How does the butterfly valve work?
The working principle of the butterfly valve is that with metal, circular disc (vane) making a rotational motion to start, stop or regulate the flow in a pipe, the butterfly valve opens, closes, or controls the flow.
2. How does the butterfly valve seal?
As we mentioned above, the valve disc makes a 90° rotation to open or close while sealing itself against the seat in the valve housing. For this reason, the sealing between the vane and the seat is essential for regulation:
A butterfly valve is a quick opening, rotational motion valve that uses a metal, circular disc (vane) to start, stop or regulate flow in a pipe. Typically, a simple 90° rotation of the valve handle either opens or completely closes the valve as the vane seals itself against the seats in the valve housing. These seals are either made with a metal-to-metal connection or to a softer, elastomeric material.
Seat: The butterfly valve seat is on the inside diameter periphery of the valve body.
To stop the flow, the butterfly valve disc seals against the seat. Basically, there are two types of butterfly valve seats, the resilient seated butterfly valve, and the metal seated butterfly valve.
Seal: To control the flow precisely, there might be three types of sealing to prevent potential leakage in different routes: flange sealing, stem sealing and disc sealing.
3. Different types of butterfly valve sealing
Based on different parameters of the butterfly valve, there can be different types of butterfly valve sealing: the concentric butterfly valve sealing vs the eccentric butterfly valve sealing; the metal seated butterfly valve vs the soft seated butterfly valve, etc.
Metal Seated Butterfly Valve:
In the case of the Metal Seated Butterfly Valve, the seat is made of metal and both sealing surfaces or the valve are made of metal material or other hard material. This design has its own advantages and disadvantages: the metal Seated Butterfly Valve is highly temperature resistant and anti-wear; on the other hand, it offers relatively poor sealing performance.
Resilient Seated Butterfly Valve
In contrary to the Metal Seated Butterfly Valve, the Resilient Seated Butterfly Valve features a soft material seat, such as EPDM seat butterfly valve, PTFE seat butterfly valve, etc. Though this soft seat may not afford high temperature or too much wear, it offers a good sealing performance: When the disc is closed, the disc squeezes the seat and deforms the seat material, and offers a squeeze type sealing.
How to choose the butterfly valve seat material? There are various factors: Is the medium corrosive? Does the medium contain abrasive particles? Is the butterfly valve of the medium of high temperature or high pressures? All of these determine whether to use a metal seat butterfly valve or a resilient seated butterfly valve.
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