Flanged and wafer-mounted gate valvesInstallation and actuator selection

01 / INSTALLATION

DN and PN do not describe the complete installation interface

In a new installation, the connection geometry can be selected together with the valve. In a modernisation project, the situation is reversed: the valve must fit in place of the existing component without forcing changes to the pipeline axis, flanges or support structure. Therefore, the actual installation dimensions must be verified in addition to DN and PN.

The flange bolt-hole pattern, bolt diameter and arrangement, sealing-face type, body thickness and access on both sides of the connection are particularly important. In wafer-mounted gate valves, the way bolts or studs pass around the body also matters. Two valves with the same DN and PN designation may require different mounting arrangements.

For knife gate valves, the dimension above the pipeline must also be considered. Opening the valve requires full knife travel, while a cylinder, gearbox or manual mechanism increases the overall height of the assembly. In practice, insufficient space above the pipeline is often the limiting factor when replacing manual actuation with an automated actuator.

02 / INSTALLATION METHOD

Flanged versus wafer-mounted gate valves

The terms “flanged” and “wafer-mounted” describe how the valve is connected to the pipeline. They do not indicate whether the gate valve uses a knife or wedge closure, nor how its seat is designed. These are two independent levels of description.

In a flanged configuration, the body has its own flanged connections that are bolted directly to the pipeline flanges. In a wafer-mounted configuration, the body is installed between the pipeline flanges and forms a much shorter component along the pipeline axis. This arrangement is typical of many knife gate valves, especially where compact design and short face-to-face length are important.

The current Metal-Gum knife gate valve range is designed for installation between flanges with a bolt-hole pattern corresponding to PN-EN 1092-1. When selecting a replacement for an existing installation, the dimensional drawing of the specific configuration should be used rather than relying only on the standard designation and PN.

03 / METAL-GUM RANGE

Metal-Gum knife gate valve range

Metal-Gum knife gate valves are intended primarily for contaminated media, deposits, sludge, slurries and media containing fibres and solid particles. The current product range uses different actuation methods selected according to diameter, load and the way the installation is controlled.

04 / LOAD

Differential pressure determines the closing load

For the actuator, the load that must be overcome during valve movement is more important than the PN designation alone. With the knife closed, differential pressure generates a force pressing the closure element against the sealing and guiding system. As DN increases, the pressure-loaded area also increases, so the required force does not scale only with the physical size of the actuator.

Friction, the nature of the medium and the condition of working surfaces add to this load. Deposits, fibres or product remaining in the chamber after a long shutdown can increase the force required to initiate movement. For this reason, a pneumatic cylinder or electric actuator should not be selected solely from a DN table.

If the valve is to operate with flow in both directions, or pressure may periodically occur on the opposite side of the closed valve, this information should also be included in the design assumptions. The direction of differential pressure can affect seat behaviour and the required operating force in a specific configuration.

05 / ACTUATOR TYPES

Gate-valve actuator types

06 / ACTUATOR SELECTION

Actuator selection starts with force and ends with automation

The energy source – manual, pneumatic or electric – is only one criterion. The first step is to determine the force and stroke that the actuator must provide under the most demanding expected operating condition. Only then can the control method, cycle time and additional equipment be selected.

1. 01gate-valve design and DN;
2. 02medium, its viscosity and content of deposits, fibres and solid particles;
3. 03working pressure and maximum differential pressure at closure;
4. 04required operating force and stroke of the closure element;
5. 05cycle frequency and expected opening and closing time;
6. 06available energy source and its actual parameters;
7. 07local or remote control and required position signals;
8. 08behaviour after loss of energy, where relevant to the process;
9. 09environmental conditions: temperature, moisture, dust, possibility of flooding or aggressive atmosphere;
10. 10space required for installation, full stroke and later service.

07 / MODERNISATION

Modernising an existing gate valve

When replacing a valve, the most useful material is not the nameplate alone but an installation drawing supplemented by photographs. This makes it possible to check body length, bolt position, access to the connection, height above the pipeline and space for the actuator.

It is also worth identifying the reason for replacement. If the previous valve jammed, had tightness problems or the actuator regularly operated close to overload, copying the existing configuration one-for-one may reproduce the same problem. Information about previous operation is therefore as important as the dimensions.

08 / SELECTION DATA

Data required for gate-valve and actuator selection

1. 01medium and information about deposits, fibres and solid particles;
2. 02operating temperature and extreme values;
3. 03working pressure, maximum pressure and maximum Δp across the closed valve;
4. 04DN, PN, standard and geometry of the mating flanges;
5. 05face-to-face length and available space above and around the valve;
6. 06required shut-off tightness;
7. 07cycle frequency and required operating time;
8. 08preferred actuator type and available power supply;
9. 09required control, limit and position signals;
10. 10required behaviour after loss of energy;
11. 11mounting position and environmental conditions;
12. 12drawing or photographs of the existing installation – for modernisation projects.

09 / COMMON MISTAKES

Common selection mistakes

• Treating matching DN and PN as confirmation that two gate valves are fully interchangeable.
• Confusing the closure-element design with the installation method: “knife” and “wedge” are not equivalents of “flanged” and “wafer-mounted”.
• Failing to verify face-to-face length, bolt arrangement and space required for full knife travel.
• Selecting the actuator only from nominal diameter without defining Δp and the nature of the medium.
• Assuming nominal pneumatic supply pressure without checking its actual value at the point of use.
• Omitting cycle count, required operating time and electric-actuator duty mode.
• Ignoring required system behaviour after loss of power or control signal.
• Failing to allow space for the actuator, cylinder removal and future service.
• Replacing the gate valve one-for-one without analysing the cause of failure or excessive wear of the previous configuration.

10 / METAL-GUM SELECTION

Selecting a Metal-Gum gate valve and actuator

For knife gate valves, the installation method and actuator should be considered as part of one configuration. The connection geometry must match the pipeline, and the actuator must provide the required stroke and force at the actual differential pressure and medium conditions. Only after these conditions are met should the control method and automation equipment be selected.

For modernised installations, it is worth providing the dimensions of the existing valve and photographic documentation of the installation location. This makes it possible to verify not only connection compatibility but also whether a larger actuator can be used, whether service access is sufficient and whether the operating method can be changed.

Technical enquiry

11 / FAQ

FAQ