Knife Valves vs Gate Valves: Which One Are Better?

Home Knife Valves vs Gate Valves: Which One Are Better?
07/09/2022
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Knife and gate valves are primarily used for on and off service in industries. They are suitable to open and close slowly to protect the device from the effects of a water hammer. Since these shut-off valves are used in applications involving heavy oil, slurries, wastewater, non-flammable viscous fluids, and clean water, people tend to confuse one for the other.

None is suitable for regulating the flow because vibrations occur when fluid pushes against a partially closed gate. It may wear and erode the seat and disk eventually. Due to such a reason, valves bought from a valve manufacturer in China should be either completely open or closed.

Although the applications of a knife and a gate valve are mostly the same, many design features set them apart. It is essential to learn about these variances to be able to pick the right one for a process application. So, let’s put the two head-to-head to know everything about knife valve vs. gate valve!

Everything to Know About a Knife Valve:

Dombor Gate Valve
Source: Dombor

A knife gate valve was initially designed for the pulp and paper industry. When stringy pulp impinges between the wedge and the sand seat to prevent flow shut-off, a knife valve is used to deal with it. It features a sharp edge to cut through the pulp and seal to deal with viscous fluids with a similar impingement risk.

This valve type is typically employed in heavy oil, wastewater, paper and pulp, and sludge and slurry industries. These devices are generally specified in larger sizes to handle viscous flows in several demanding applications.

Primary Advantages of Using a Knife Valve:

  • It is easy to actuate and light and is available in several affordable options.
  • It is best for applications with viscous fluids as its blades can easily cut through thick liquids.

Despite these advantages, a knife valve may sometimes cause significant inconvenience to the users.

Some Disadvantages of Using a Knife Valve:

  • It is widely known for its low-pressure limitations.
  • It is a less-desirable shut-off valve for applications requiring cleanliness and optimal hygiene conditions.

The function of a knife valve diminishes when used in dry bulk applications. Its blade fits into an elastomer seal after it cuts through the media. Over time, the seal becomes abraded and may influence the sealing performance, leading to downtime, decreased production, and negatively impacting revenue streams.

Everything to Know About a Gate Valve:

Dombor Knife Gate Valve
Source: Dombor

As opposed to flowing regulation operations, a gate valve is often used for shut-off operations as it offers only on and off settings to a user.

A butterfly gate valve operates by lifting a round or a rectangle-shaped gate from the path of the media, typically fluids. The sealing surface lying between the gate and the seats is called planar. It is often suitable for applications requiring a straight flow of fluids with minimal restrictions. It has a flat closure that slides in or out, up or down between the two parallel plates to open or close.

It is widely used in oil and gas, pharmaceuticals, automotive, power plants, mining, offshore, general process manufacturing, and water treatment.

Primary Advantages of Using a Gate Valve:

  • The pressure drop is shallow when the valve is fully open.
  • It is used as a shut-off device and to perform bi-directional action.

Although a valve bought from gate valve manufacturers is a valuable device in industries, it has some downsides too.

Some Disadvantages of Using a Gate Valve:

  • It requires a large amount of force to operate and may even need automatic actuators to function.
  • It is not the quickest valve to perform the open and close function.
  • It is not ideal for space-sensitive applications as it takes up a lot of space.
  • It is prone to thermal expansion and shrinking when exposed to high-temperature variations.

Learning Everything About Knife Valve vs. Gate Valve:

Industrial Pipes
Source: Unsplash

Here is a table to learn about knife valve vs. gate valve available at a reliable industrial valves company:

BASIS OF DIFFERENCEKNIFE VALVEGATE VALVE
DESIGNA knife valve features a sharpened disk to sever any stringent solids that may keep it from closing and causing leaks.A gate valve features a flat closure sliding in and out, up and down between parallel plates to open and close it.
PACKING GLANDA knife valve has a packing gland to seal around the gate.A gate valve has a v-ring packing set to seal the shaft attached to the gate.
DIMENSIONSA knife valve is available in either wafer or lugged body with no flangs.A gate valve is wider, flanged, ANSI pressure-rated, and has API leak tightness.
PROFILEIt has a thin profile.It has a bulky profile.
STANDARDSIt is built to TAPPI standards.It is built to ANSI standards.
DIRECTIONKnife valves are uni-directional.Gate valves are bi-directional.
WEIGHTA knife valve weighs far less than a gate valve.A gate valve weighs a lot more than a knife valve.
COSTIt is a cost-friendly option compared to its counterpart.It is an expensive option compared to its counterpart.
TYPICAL APPLICATIONIt is widely used in sludge and slurry, paper and pulp, wastewater management, and heavy oil industries.It is widely used in oil and gas, automotive, power plants, mining, process manufacturing, offshore, water treatment, and pharmaceuticals.
AVAILABILITYIts seat comes in metal to resilient types.It is only available with metal seats.

In brief, a knife valve employs a blade to cut through thick fluids, while a gate valve uses a slide plate to shut off the flow of dry bulk material. The sharp and beveled edge of a knife valve makes it ideal for large-sized applications involving varnish, paper pulp, light grease, and wastewater. Its easy actuation and low cost make it perfect for several industries.

A China actuated gate valve is perfect for handling dry bulk powders, pellets, and granules. It has a flat, rectangular slide plate to shut off or permit dry material flow. It actuates between two compressed-loaded, rigid polymer plates reinforced by a compressed, hard rubber.

When the gate experiences frictional wear to the rugged polymer seals from several actuators over time, its rubber backing ensures the seal constantly forces against the slide plate. But sometimes, the hard polymer seals may wear and lose their effectiveness. When it happens, the bolts may loosen, and remove shim along each lateral aspect of the gate to re-tighten the bolts. It will help restore the compression load of the gate.

Parting Thoughts

Hopefully, this article helps everyone learn about knife valve vs. gate valve to pick a suitable option according to the application.

When quoting the ideal valve for a facility, it is vital to consult a reliable manufacturer who offers these valves at an affordable price. Depending on the media flowing through the device, valve quality, and application, a user must select the correct valve. It will help save replacement costs for the future. To buy these valves in high-quality and at an affordable range, please contact us.

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