If you maintain gate valves, you have probably had this experience: two valves with the same DN, but only one of them fits the grinding machine you have.
That is not necessarily a fault in the machine. It usually points to the selection step: DN — the nominal size — tells you roughly how big the valve is. It does not tell you what the machine actually has to work on.
Here are the three checks that decide whether a machine fits, and why each one matters more than DN alone.
This is the number that matters most. The machine's grinding range must cover the diameter of the sealing face itself — not the pipe bore, not the flange size, not the DN on the nameplate.
Two gate valves can share the same DN and still have different sealing-face diameters, because pressure class, standard, and manufacturer all change the seat geometry. A machine that covers one DN400 valve may not cover the next DN400 valve on the same line.
Our portable gate valve grinder, the M-300C, has a grinding range of Φ118–430 mm for DN100–400 (4″–16″) gate valves. If your sealing-face diameter falls within this range, the M-300C may be a suitable option. If your sealing-face diameter falls outside this range, the M-300C should not be selected without further technical confirmation. The valve geometry, required working depth, and available installation space must also be checked before confirming suitability.
Measure the sealing face, not the valve label.
Before selecting a machine, check your required working depth against the machine's stated specification. The M-300C manual lists 850 mm under the field "maximum grinding depth." Because the manual does not further define how that depth is measured, confirm it against your required working depth with the supplier before deciding.
Confirm the depth, not just the model.
This is an important check that can be overlooked during machine selection, especially for on-site maintenance. Two parts need attention:
Minimum spacing between the sealing surfaces. The machine has to fit between the faces it is grinding. If the gap is too tight, the machine may not be set up properly. For the M-300C, the manual lists a minimum spacing between sealing surfaces of 55 mm. This is a separate specification from "minimum valve opening"; the two should not be used interchangeably.
Installation space around the valve. For in-situ work — where the valve stays in the line and the machine is brought to the valve — there has to be room to lift and position the machine, place the drive unit, connect power, and work around nearby pipework and obstructions. A machine that fits on paper but not in the pipe rack is no use during a shutdown.
This is also why in-situ grinding is used: a valve welded into the line cannot always be removed for workshop repair. The M-300C weighs 78 kg and may be considered for on-site work when the valve geometry and installation conditions are suitable. The available space and access must be checked before confirming the application.
Check the space before the shutdown.
If you are checking a machine for a specific valve, please share these five details instead of just the DN:
Sealing-face diameter
Minimum spacing between the sealing surfaces
Required working depth
Available installation space around the valve
Available power supply and relevant site conditions
A photo of the valve and the damaged sealing face can help with a preliminary assessment, but it does not replace measurements. Please also provide the key dimensions or a valve drawing where available.
These details can help narrow down the model at a preliminary stage. Final confirmation still requires checking the valve geometry, required working depth, installation space, power supply, and site accessibility.
DN is where selection starts. It should never be where it ends.
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