What is a guillotine valve?
They are a variant of gate valves with a simpler and more economical construction.
They are particularly suitable for low pressures.
They can be built in very large diameters and in various shapes, such as square and rectangular, and are used in canals and dams.
Their applications range from solid products to water and pastes. It is in the latter application where their effectiveness is greatest and they have become the king of sectors such as paper mills, silos for solids and large-diameter water pipes.
We can find them with fixed and ascending spindle, the seal can be soft with NBR, EPDM, VITON etc. seals and with metal-to-metal seals for use with solids and powders such as flour, etc.
The soft seals are called watertight types.
The guillotines with metal-to-metal seals are not watertight, they have a small percentage of leakage, it is recommended not to use them with liquids.
TYPES OF KNIFE GATE VALVES
- SEALED (those that incorporate a gasket in their sealing)
- NON-STARS (Metal-to-Metal seals)
- FIXED SPINDLE
- RISING SPINDLE
- ROUND FOR FLANGES
- SQUARE AND RECTANGULAR these can be watertight on 3 or 4 sides depending on whether they are for a duct or a channel.
- UNIDIRECTIONAL (closes only in one direction)
- BIDIRECTIONAL (closing on both sides)
KNIFE GATE VALVE MATERIALS
The most common materials for the construction of the bodies are:
- GREY or NODULAR CAST IRON
- CARBON STEEL
- STAINLESS STEEL
The sluice gates are always made of stainless steel.
STAINLESS STEEL AISI-304 (for cast iron or steel body)
STAINLESS STEEL AISI-316 (for stainless steel body)
Alloy steels can also be used for high temperature applications.
Special steels such as Duplex or Superduplex for seawater applications.
KNIFE GATE VALVE CONNECTIONS
AUTOMATIC ACTUATION
Although they are of the multi-turn type, their automation is simple as they have a low operating torque.
PNEUMATIC VALVES
Their pneumatic automation is very competitive in price, as the valve manufacturers themselves incorporate a pneumatic cylinder on top of the valve.
This point is of great importance as they leave the factory with the actuator mounted and adjusted, even in large diameters.
This is not the case for valves of any other type where the manufacturer of the valve and the actuator is usually not the same.
The most common are DOUBLE EFFECT and SINGLE EFFECT.
MANUAL ACTUATION
- The most common types of actuators for this type of valve are:
- STEERING WHEEL
- MANUAL REDUCER (for large diameters)
- MANUAL REDUCER WITH CHAIN (for valves at height)
- QUICK LEVER (for when we need to close or open quickly)
The use of shaft extensions is also very common in this type of valves, to which we can later mount a handwheel, gearbox or automate electrically.
ELECTRICAL
In electrical automation, there are models with a coupling flange for mounting the motor.
The motors shall be of standard multi-turn type, from any manufacturer on the market.
ACCESSORIES
As accessories, they can be fitted with limit switches, inductive sensors, solenoid valves, pneumatic and electro-pneumatic positioners, etc.
DEFLECTORS
In order to prevent particles from becoming embedded in the valve guides, we can incorporate scrapers and deflectors.
Another application is the use of "V" baffles to convert the knife gate valve into a control valve together with a regulating motor.
APPLICATIONS AND RECOMMENDATIONS
Although we have already mentioned their applications throughout the explanation of knife gate valves, we would like to emphasise the fact that they are the king of large diameters. Their simple and economical construction makes them very competitive in large DN.
Applications in solids and powders are also one of their great virtues. They can be built to Atex standards for these applications.
Slurries, slurries and mining are perhaps the applications where their characteristics make them the most widely used valves.
As a recommendation, they are not good friends of high pressures and temperatures.
