5 Different Ball Valve Seal Surface Design
In ball valve industrial, the most important component for the ball valve to seal the pressure inside the fluid control system is the valve seat or the valve sealing face. The ball will cooperate with the ball seat to seal the pressure. In different control system, it will has different medium, so valve design engineer need to adapt different valve seat or different ball valve seal surface to seal the pressure using different engineer material. This article will show 5 different ball valve seat design.
First kind of ball valve seat is one kind of soft seat ball valve seat. Usually the color of this seat is white and are widely use in soft seat ball valve industry. This white seat made from PTFE. The advantage of this seat is made by engineering Teflon and when we are going to assembling this kind of valve seat and the ball inside the valve body. When we are going to compress the valve seat with the ball, this kind of cooperation are very easily to seal the pressure inside the flow control system. However the disadvantage is because the valve seat is not metal and soft so if the fluid are not pure and contain a little particle inside, the particle may damage the ball valve seat and make the valve leak so engineer are looking for another kind of material which is harder than this kind of soft seat material and also the material is elastic material.
So what kind of material has that property? In ball valve industrial, engineers develop some other color. These different color seat are coming from Rein-force PTFE material. The purpose of develop these colored seat material is we need improve PTFE application temperature for higher. So engineers mix other kind of material with PTFE to make new kind of material.
The first improve PTFE is with carbon mixed PTFE To make one kind of this seat. The color is black.
Another is PTFE mix with stainless steel. This type material seat has two advantages compare to pure PTFE seat. One is it can work in high temperature through control system than before. The other is the material hardness is much better than before. Basically this material is much harder than the pure PTFE. So the particle inside the flow media are not so easier to damage the ball valve seat compared with PTFE. So these two kinds material is another kind of valve seat in soft seat ball valve industry.
Soft seat ball valve is one kind of valve which is very easily to get zero leakage function because the valve seat is one kind of elastic material but this kind of design had one disadvantage which is if the fire occurred, the fire can totally destroy the valve seat. So if one manufacture is a flow control system or use soft seat ball valve, if the fire happen, all the flow medium will get leak so there will be very dangerous so engineer want design one kind of valve seat which is soft seat but it can resist fire risk and this called fire-safe design according to API 607.
In soft seat ball valve industry, whatever kind of material you are going to use to make the ball valve seat if the fire occur, the high temperature will totally destroy the ball valve seat, the valve will be leak so that will be very dangerous situation so in soft seat ball valve industry, fire safe design are very important. The original seat which is cooperated with the ball to seal the pressure. When the fire occurred the high temperature totally destroyed the original seat because the flow control system do have the pressure inside, the pressure will push the ball flow to the downside. So valve design engineer designed second seal surface. It actually this second seat is one part of the valve body. It is metal material so it will not destroyed by the high temperature. And also the second valve seat, the seal surface is very limit so it is very easy to cooperate with the ball to seal the pressure inside the flow control system. Even though in this condition, when the pressure push the ball to cooperate with the second valve seat to seal the pressure inside the flow system, the ball valve cannot operate again but at least the flow media inside the flow control system still safe. So this kind of design we call the fire safety design.
Next ball valve seat design is metal to metal seat. When we talk about metal seat in ball valve industry, actually we have two kind of metal seat. One is metal seat with soft material insert like picture below.
This type mainly seat is made by metal material, the stream going to push the seat to touch the ball to seal the pressure but actually the sealing surface the valve seat which the area going to touch the ball are not metal because we are going to insert soft seat material inside the metal seat. The area going to touch the ball to seal the pressure inside the flow control system. The metal seat just a frame which going to protect the real valve seat to touch the ball to seal the pressure. This type seat design work in big size ball valve and have high performance in application because the soft seat material is easily to be damaged in big size. The metal seat to protect the soft material inside under this area.
There is another true metal to metal seat of the ball valve. The ball valve seat are totally made by metal and the metal seat will cooperate with the metal ball to seal the pressure inside the flow control system. This kind seat of design ball valve can work in very high temperature and very high pressure environment but this kind of design difficult to produce because the ball and seat need to very accurate machined and grind. Because the valve seat are totally made by metal so the ball must harder than the seat. If the ball softer than the ball seat, then the valve seat will scratch the ball and make the ball valve leakage. Whatever the ball valve seat you are going to design, the sealing surface the wider must be harder than the narrow sealing face. This metal seat ball valve a little bit special because it is designed two line for the valve seat sealing surface. This two line sealing surface can make this valve sealing are more reliable. To make the ball are harder than the valve seat. Most time we are going to use several different treatment to make the ball are harder than the valve seat.
The last one is lined ball valve. This kind of ball valve are very special and other kind of ball valve. In some kind of special flow control system, the flow media are very corrosive, we even can not use metal to touch the flow media, so we are going to use PFA or PTFE or other kind of material totally cover the ball and also cover all the area which going to touch the flow media.