Hello guys, yesterday we have discuss the gate valves on my desk with co-workers. Our discussion drives into a debate because one of us disputes that the gate valves and knife edge gate valves are the same and just knife edge gate valve has a sharp knife edge while the other one comes up as, “No they both are different.” So we agree to find out the similarities and differences between both valves. So let’s start to explore them.
Similarities of Both Gate Valves
The primary application of gate valves and knife edge gate valves is the on/off control. As a result, it is not recommend to use these types of valves for flow regulation since fluid can push against a partially closed gate, causing a vibration that wears down the disk and seat over time. As a result, valves of this type ought to be either completely open or completely closed.
Valve opening and closing are also design to be slow to prevent water hammer damage.
Both gate valves can be found in the following applications:
- Heavy oils
- Clean water
- Non-flammable viscous fluids
Differences between Both Gate Valves
There are vast differences between them. First of all, the knife gate valve does have a sharpened disk. It is meant to cut through any stringent solids that might hinder the valve’s ability to close and cause it to leak. Their designs differ on more than one level as well.
The biggest difference between the gate and knife edge gate valves is that gate valves adhere to ANSI standards, whereas knife gate valves adhere to TAPPI standards. Dimensionally, the gate valve is wider, flanged, and pressure rate to ANSI standards. Furthermore, it must meet API leak-tightness standards. Their bidirectional nature makes them applicable to both steam and fluid. Metal seats are the only option for gate valves.
A knife gate valve is also different from an ANSI gate valve in regards to the packing gland. In gate valves, the shaft attached to the gate is sealed with a v-ring packing set, while in knife gate valves, the gate is sealed with a packing gland.
When compared with its bulkier counterpart, a knife gate has a much thinner profile. Furthermore, it’s unidirectional (although some are bidirectional), and comes as a wafer or lugged body, with no flanges. The knife gate valve seats can be made of metal or resilient material.
The two biggest advantages knife gate valves have are their weight and expense. An ANSI gate valve weighs over 1200# while a knife gate valve typically weighs less than 300#. Valve cost also varies greatly depending on the weight.
After this research, we finally know that sharpness is not the only difference between the gate valve and the knife edge gate valve.