We all know that the gate valve is the most common valve used to cut off , The knife gate valve and gate valve difference is that it has a blade shape valve disc, the blade has good cutting performance, at the same time, the knife gate valve has a very good ability to clean the sewage, so commonly used in the pipeline containing solid particles, fibrous material or viscous substances, such as sewage treatment, powder, paper, mining and other industries.
How to Choose The Type of Knife Gate Valve?
According to the characteristics of the substances, you can choose different types of knife gate valves, such as ordinary knife gate valve for solid particles and fibres, suspended substances, penetrating gate valve is suitable for easy to block the switch of the substances and slagging system, square knife gate valve is more suitable for slagging system, double knife gate valve is suitable for the requirements of the rapid switching and sealing requirements are not strict system.
Different types knife gate valve
How to Choose The Knife Gate Valve Body and Disc Material？
For knife gate valve body and disc，the commonly used material is ductile iron, carbon steel and stainless steel.
Ductile iron is more corrosion-resistant compared to carbon steel, but can only be used for low-pressure pipelines, so it is commonly used in sewage and other municipal projects. Compared with ductile iron knife gate valve, carbon steel knife gate valve is not corrosion-resistant, but high pressure and high temperature resistance, so it can be used for oil, natural gas and other high-pressure or high-temperature project. For some corrosive fluids and gases, you should choose stainless steel, copper and other corrosion-resistant valve body materials.
How to Choose the Knife Gate Valve Sealing Method?
Knife gate valve is divided into unidirectional sealing and Bi-directional sealing , For solid substance unidirectional sealing is enough, but for liquid, you needs to choose Bi-directional pressure sealing, in order to prevent the liquid backflow.
Knife gate valves are divided into resilient seated and metal seated.
Among them, the sealing material of resilient seated is usually elastic material such as rubber or plastic, and the sealing surface made of this material can fit the piston or valve seat to achieve good sealing performance. The knife gate valve metal seated sealing material is commonly used metal or ceramic and other hard materials, this material can withstand higher pressures and temperatures, but the sealing performance is relatively poor.
Resilient Seated Knife gate valve has good sealing performance, can prevent the substance leakage, but the sealing surface is easy to be fluid scouring and wear, and in high temperature, high pressure and other harsh conditions may fail. On the contrary, the metal seated knife gate valve has poor sealing performance, but can withstand higher temperatures and pressures, and the sealing surface is not easy to be affected by external factors.
Resilient seated knife gate valve is suitable for low pressure, low temperature, general substance and easy to seal the surface of each other, such as tap water, air, oil, etc.And metal seated knife gate valve is suitable for higher pressure, higher temperature, strong corrosive or viscous substance occasions, such as sewage treatment, chemical industry and other fields.
How to Choose The Packing of Knife Gate Valve?
- You should try to choose a small friction coefficient packing , such as PTFE material packing have smaller friction coefficient than graphite packing, the small friction coefficient packing, can reduce the friction of the valve, improve the service life of the valve.
- The number of layers and length of the packing is not the more the better, usually, the length of the packing is 1.5 times of the stem diameter.
- The packing structure, should have the function of adjusting the compression force, in order to compensate for other factors such as wear and tear caused by the decline in sealing.
Is the Guide Ring Necessary?
The guide ring can prevent the liquid from stagnating in the valve cavity, so for some corrosive and abrasive media, the guide ring is necessary.
PTFE limit block
Ensure that the gate is not in contact with the valve body, prolonging the service life of the gate.
Need to choose lined knife gate valve?
PTFE lined knife gate valve, PTFE lining can play the role of lubrication, so that the switch is more energy-saving, if you need a knife gate valve with small torque, you can choose PTFE lined knife gate valve. Good PTFE surface is brighter, good resilience, tight structure, good sealing.
For some special working conditions, such as iron ore, copper ore, gold ore, etc., the wear resistance of the knife gate valve is very high, this time you need to choose polyurethane lined knife gate valve, to ensure that the slag will not touch the sealing surface, which reduces the wear and tear of the slag on the sealing surface to ensure that the valve seals and O leakage.
How to Choose Knife Gate Valve Actuator?
Knife gate valve can be operated by manual (hand wheel or gear box), electric, pneumatic, hydraulic and sprocket switch.
Electric knife gate valves, which can be controlled by Bluetooth and mobile phone app, can remotely control the valve switch and flow rate.
What Coating or paint to choose?
Ductile iron and carbon steel knife gate valves require anti-corrosion treatment on the surface. Anti-corrosion treatment normally include FBE coating and cold spray painting. The difference between the two is that the FBE coating has good adhesion and is not easy to fall off. And cold spray paint is easily scratched off. The thickness of FBE coating can reach hundreds of microns, while the thickness of cold spray paint is only tens of microns or less. So the performance of FBE coating is far better than cold spray painting, and the cost of FBE coating is higher than cold spray painting.
Knife Gate Valve Connection
Knife gate valve connection include wafer, lug and flange. The wafer can be connected in the middle of the two flanges, lug is generally used for the end of the pipeline, with bolts and flange connection, flange refers to the two flanges at both ends of the knife gate valve, through the flange for connection.
Knife Gate Valve Flushing Device
In the case that the substances may enter into the valve cavity, you can install a flushing device to flush, thus extending the service life of the knife gate valve and ensuring the good sealing performance of the knife gate valve.
The Following Are Examples of Knife Gate Valve Selection
- For water, the normal resilient seated knife gate valve can be used. If the water contains trace particles, but no need very good sealing performance, you can choose metal seated body; if you need good sealing performance, you can choose PTFE or polyurethane .
- For cement mixture, square plug valves can be chosen for dry material at the casting outlet. If the sealing requirement of wet and dry material in the pipeline is not high, you can use the metal seated body; if the sealing requirement is high, you can choose PTFE or polyurethane
- For plastic particles, generally choose the metal seated body , 201 valve disc. Nitriding treatment can be used for better wear resistance, but the sealing performance after treatment is worse than the metal seated one.
- For coal, if you consider the corrosion of sulfur, you can choose SS304 body with metal seated; if you do not consider the corrosiveness of conventional, only metal seated is enough, no need SS304 body . The sealing material for coal slurry should use polyurethane.
Judberd is professional manufacturer for knife gate valve, if you need good performance knife gate valve, or you need help to choose the right knife gate valve.Contact judberd.
Stainless steel knife gate valve
Wafer type carbon steel knife gate valve
Pneumatic Operated Flange Knife Gate Valve
