An Introduction of Bellow Seal Gate Valves | EN | ES

An Introduction of Bellow Seal Gate Valves

A bellow seal gate valve has the disc in the shape of a plug, the conical or flat sealing surface as well as the valve clack with motion along the centre line of flows.

The motion type of the bellow seal gate valve can be divided into the rising stem type (only the valve stem moving up and down and the hand wheel not), and the rotary stem type (the nut mounted on the valve body and the valve stem rotating up and down together with the hand wheel). 

A bellow seal gate valve can only be fully opened and closed, and can not be used to regulate or throttle the flow. Moreover, it should be installed horizontally in pipelines. 

The bellow seal gate valve has short opening and closing strokes, and shows good performance to block the media. Besides, this kind of valve is extremely suitable for the adjustment of flows because the diameter of the valve seat's port is in direct proportion to the clack's stroke. Thus, the gate valve is adaptable to blocking and regulating the media especially.

Cautions for installations of bellow seal gate valves
The position and height of the valve should reach the design requirements.

All the joints have to be firmly connected. 

The appearance of the bellow seal gate valve should be examined by the valve manufacturer before installation. In China, the data plate of the valve needs to reach the regulation of the current national standard BG1220. With the working pressure up to 1.0 MPa, the valve operated to block the flow needs to go though strength tests and sealing tests, and can be put into use after qualifying.

The strength test of the valve should last for not less than 5 minutes and the test pressure should be the 1.5 times of the nominal pressure. During the test, if the filter and the valve body do not leak, the valve is qualified.

During the sealing test, test pressure is 1.1 times of the nominal pressure. The duration of the test must reach the requirement of the national standard GB50243. The valve is recognized as the qualified product if the sealing surface of the valve clack do not leak.

Advantages of bellow seal gate valves
Simple structures, easy production and maintenance
The short valve stroke with short time of opening and closing
Great sealing performance, small friction between sealing surfaces, the long operation life

Disadvantages
Great flow resistance demanding more strength to open and close the valve
Not suitable for the easy-coking media, media with particles or high viscosity 
Poor regulation performance