Five steps to design a API600 gate valve

How the engineer design a API600 gate valve by standards?

Step1: Flange dimensions

      We need to design the flanges, according to API600, the flange is as per ASME B16.5 including the OD, PCD, gasket height and gasket diameter, thickness etc.

Step 2 Face to face dimensions and wall thickness

For the face to face dimensions, look up the ASME B16.34

For the wall thickness, look up the API 600

Step 3 This step we are going to design the valves gate and seat ring.

First, we talk about the valve seat, the inside diameter is same as the ID of flange. The width of seat is 10mm for each side. For example DN100, the inside diameter is 102, seat width is 10mm so the OD of seat ring is 102+10*2=122mm. When it comes to seat face, it varies according the sizes, begining from 5mm.

Second, we will design the gate, when the valve open and close, the seal face of gate and seat ring scratch to each other. As the cycle time increases, the seal face of both seat ring  and gate going thinner and the gap between the two seat rings will be wider. That will cause the gate goes down. The gate goes down until the seal face can not touch the seat ring and the gate valve leaks. So the API600 has the rules for the wear travel, which is the distance the seal face of gate wider than the seal face of seat. It also means the distance goes down until it can not seal with seat seal face. 

The minimum gate seal face is seat seal face width +wear travel.  For a better quality, we use 2 times of wear travel to increase the long service time.

Another thing is the bottom gate width.The bottom gate width= valve wall thickness *1.5

For the bottom cavity, it needs to have enough space for the wear travel of gate. Usually, we double the wear travel, that is: the bottom cavity=2* wear travel.

Step 4 Valve cavity diameter

The valve cavity is to provide enough space for the gate goes up and down. Usually 8-10 mm larger than the size of the gate.

Step5 Dimensions of middle flange

The main principle of designing the middle flange is that the middle flange do not interference with the side flanges so that the lathe can machining the back of flanges easily. As a general rule, the middle flange is usually 18mm higher than the side flanges.

As per the dimensions, some may think that we design the middle flange same as the side flanges. But it is impossible since it will interface with the side flanges. But since the middle flange also hold the working pressure same as the side flanges. So here is the principle:

For the bolt holes , the size is usually one lever smaller than the side flange, for example,φ25 for side flange, thenφ22 for middle flange;

For the bolt quantity we use one level higher than the side flanges, for example, 8 holes for side flanges, then 12 holes for middle flange;

For the thickness, we keep it same as the side flange.