INDUSTRIAL VALVES
Industrial gate valvesSelection of design, materials and operating parameters
Knife gate or wedge gate design, wetted materials, differential pressure and actuation
Selecting an industrial gate valve starts with the nature of the medium and the way the installation operates. DN and PN designations help define the connection conditions, but they do not determine how the valve will behave with deposits, fibres or abrasive particles, nor the force required to close it at a given differential pressure. The materials of the wetted parts, seat design, required tightness level, mounting position and actuation method are equally important.
In practice, a gate valve operates as part of a specific process node. The same nominal diameter may require a different configuration in contaminated-water service, mineral slurry, sewage sludge or chemical media. The process description should therefore come first, followed by the selection of design and materials.
01 / DESIGN
Gate-valve design and the nature of the medium
Knife gate valve
A knife gate valve uses a plate that moves transversely through the flow path. This geometry is well suited to installations where the medium contains deposits, fibres, suspensions, sludge, slurries or other components that make it difficult for a conventional closure element to seat correctly. Depending on the configuration, the knife can pass through a layer of deposits or fibrous medium, while the chamber design can reduce accumulation in the closing zone.
Wedge gate valve
A wedge gate valve operates differently: closure is achieved by seating a wedge against the seat surfaces. In typical applications it is selected primarily where the medium is clean or relatively clean and where the installation geometry and process conditions do not cause material to build up in the sealing zone. With a higher solids content, the seat area becomes one of the key points to assess.
The terms “knife” and “wedge” describe the closure principle, whereas “flanged” and “wafer-mounted” describe the installation method. These are independent valve characteristics and should not be used interchangeably.
Gate valves of this class are selected primarily as isolation valves. If the valve is expected to operate for long periods in an intermediate position or perform a throttling function, this mode of operation should be considered when selecting the specific configuration.
02 / METAL-GUM RANGE
Metal-Gum knife gate valves
The current Metal-Gum knife gate valve range includes configurations intended for isolating contaminated water, wastewater, deposits, sludge, slurries, fibrous media and semi-liquid media. The design and materials are selected for the conditions of the specific installation.
| Parameter | Range / configuration |
|---|---|
| Nominal diameter | DN50-DN1000 |
| Range / connection designation | PN10 |
| Operating temperature | -10 °C to +120 °C – depending on configuration |
| Body | cast iron / carbon steel / stainless steel |
| Knife | stainless steel 1.4301 / 1.4404 |
| Sealing | EPDM / NBR / soft profile |
| Actuation | manual / electric / pneumatic / remote linkage |
| Installation | wafer-mounted, bolt-hole pattern according to PN-EN 1092-1 |
These values describe the product-family range. They must not be combined into a single extreme operating point. Permissible pressure, differential pressure across the closed knife, temperature and material configuration must match the specific DN and valve configuration.
03 / INSTALLATION
Installation and connections
When replacing existing valves, matching the DN alone does not guarantee interchangeability. The flange spacing and bolt-hole pattern, sealing-face type, body thickness, face-to-face length, and the space required for full knife travel and actuator operation must all be checked.
In a wafer-mounted gate valve, the body is installed between the pipeline flanges. This provides a short face-to-face length, but requires compatibility of the complete connection: mating flanges, bolts, seals and the way the valve is supported. The current Metal-Gum knife gate valve range is designed for wafer mounting with a bolt-hole pattern according to PN-EN 1092-1.
For modernisation projects, service access should also be verified. The actuator, stem and extending knife may require significantly more space than the body installed between the flanges.
04 / MATERIALS
Wetted materials and aggressive media
The term “acid-resistant gate valve” is used commercially, but from a technical selection perspective it is too broad. Valve resistance is not determined by the body material alone. All parts in contact with the medium must be assessed: the knife, seat, elastomers, guiding components and other wetted surfaces.
The Metal-Gum range includes bodies made of cast iron, carbon steel and stainless steel, as well as knives made of stainless steel 1.4301 or 1.4404. The steel grade alone still does not replace information about the medium. Selection requires knowledge of its composition and concentration, temperature, the presence of chlorides or other corrosion-relevant components, and the share and abrasiveness of solid particles.
The seal material is equally important. EPDM and NBR differ in chemical and temperature resistance and in their behaviour in contact with oils, fuels or water. The elastomer must therefore be selected for the actual medium rather than treated as a standard addition to a particular body material.
05 / PRESSURE AND Δp
Pressure, differential pressure and tightness
The PN10 designation should not be interpreted as meaning that every valve in the range can operate with a 10 bar differential pressure across a closed knife. For isolation valves, the connection and body pressure class must be distinguished from the maximum differential pressure at which a particular configuration maintains its intended closing function.
As DN increases, the forces acting on the closure element increase, so the requirements for knife design, guiding, sealing and actuation also change. The documentation for the specific configuration should be checked for permissible working pressure and Δp at closure, particularly for larger diameters.
The required tightness should also be stated in the technical enquiry. “Closed” does not always mean the same permissible leakage in every application. If the project or process specifies a particular leakage class, acceptance test or test conditions, that requirement should be established before selection and quotation.
Flow direction can also matter. Some designs are symmetrical, while others have a preferred seat-loading direction. If reverse flow occurs or pressure can appear on either side of the closed valve, this should be included in the design assumptions.
06 / ACTUATION
Actuation and control
The gate-valve actuator is selected according to the required closing force, cycle frequency and method of operating the installation. A handwheel is suitable for occasional operation and good valve accessibility. Electric or pneumatic actuation is used where remote control, process automation or a defined operating time is required. Remote-linkage configurations are also possible in locations that are difficult to access.
Actuator selection should not be based solely on DN. The load is affected by differential pressure, seal friction, deposits, the time spent in one position and the nature of the medium. For automated actuators, the control method, position signals, available power supply, environmental conditions and required behaviour after loss of energy must also be specified.
07 / SELECTION DATA
Data required for gate-valve selection
For a typical application, unambiguous selection requires a description of the medium, process conditions and method of operating the valve. A technical enquiry should include:
- the medium, its composition and concentration;
- the content of deposits, fibres, suspensions and solid particles and, where relevant, their abrasiveness and size;
- operating temperature and minimum and maximum values;
- working pressure, maximum pressure and maximum differential pressure at closure;
- required tightness and any acceptance-test requirements;
- DN, PN and connection standard;
- available face-to-face length and space above the valve;
- flow direction and the possibility of pressure occurring on both sides of the valve;
- cycle frequency and required operating time;
- actuator type, control method and available power supply;
- mounting position, environmental conditions and service requirements.
When replacing an existing gate valve, it is useful to include a drawing or photographs of the installation and information about the reason for replacement. Seat wear, knife jamming, excessive closing force or medium build-up may indicate that the problem was not caused solely by the age of the valve, but by a mismatch between the design and the process conditions.
08 / COMMON MISTAKES
Common selection mistakes
- Selecting only by DN and PN without defining the nature of the medium and the actual differential pressure.
- Treating PN10 as equivalent to a permissible Δp of 10 bar across the closed knife for every DN and configuration.
- Omitting fibres, deposits, solid-particle size and abrasiveness.
- Selecting material based only on the terms “stainless” or “acid-resistant” without checking all wetted parts.
- Ignoring flushing, cleaning, shutdown and other transient process states.
- Selecting the actuator solely by nominal diameter.
- Ignoring face-to-face length and the space required for service and full knife travel.
- Replacing a valve one-for-one without analysing the cause of previous wear or jamming.
09 / METAL-GUM SELECTION
Selecting Metal-Gum industrial gate valves
For installations carrying contaminated or fibrous media, sludge and slurries, a knife-gate design is usually the starting point. The correct configuration is determined by the process conditions: medium composition and abrasiveness, temperature, pressure and differential pressure, required tightness, wetted materials, installation arrangement and control method.
When modernising an existing process node, it is also worth providing the dimensions and documentation of the current valve. This makes it possible not only to retain connection compatibility, but also to assess whether the new valve should operate under the same conditions or solve a problem present in the existing configuration.
10 / FAQ
FAQ
Is a knife gate valve suitable for media containing deposits and fibres?
Such media are typical applications for knife gate valves. Final selection still depends on the amount and nature of solids, abrasiveness, temperature, differential pressure and the seat and sealing design.
Does PN10 mean operation at a differential pressure of 10 bar?
This should not be assumed automatically. The PN designation describes the nominal class of the range and connections, while permissible working pressure and differential pressure across the closed knife depend on the specific model, DN and configuration.
Is a stainless-steel body sufficient for aggressive media?
No. All wetted parts must be assessed, particularly the knife, seat and elastomers. Selection should be based on the actual composition, concentration and temperature of the medium.
Can every knife gate valve use any actuator?
No. The actuator is selected as part of a specific assembly, taking into account DN, required force, differential pressure, cycle frequency, environmental conditions and control method.
When replacing a gate valve, is it enough to provide DN and PN?
No. Information about the medium, pressure and Δp, required tightness, connection configuration, installation dimensions, actuation method and available service space is also required.