Portable Gate Valve Grinding & Lapping Machine Manufacturer
A gate valve that leaks after a good overhaul usually has a seat problem, not a packing problem. Throttled flow cuts wire-drawing marks into the sealing faces, scale and weld debris scratch them, and years of heat cycles leave the seat and wedge slightly out of flat. Re-grinding them in place, with the valve still in the line, is often faster than pulling the valve out.
Metals Kingdom's M and MZ machines are built for that job. Seven standard models cover DN50 to DN1200 and grinding diameters from Φ60 to Φ1330 mm, as part of our portable valve grinding machines range. The real selection question is which machine fits through your valve's opening and reaches your seat. We have built valve maintenance equipment since 1994 and can add special tooling when the standard setup does not match.
How to Choose a Portable Gate Valve Grinding Machine
Model | Valve Size | Grinding Diameter | Motor | Weight |
|---|
MZ-150 | DN50–150 | Φ60–195 mm | 850 W | 38 kg |
M-200 | DN80–200 | Φ95–225 mm | 1300 W | 70 kg |
MZ-250 | DN90–250 | Φ95–270 mm | 1300 W | 45 kg |
M-300C | DN100–400 | Φ118–430 mm | 1300 W | 78 kg |
M-600 | DN200–600 | Φ225–630 mm | 1300 W | 80 kg |
MZ-900 | DN400–900 | Φ400–960 mm | 1150 W | 270 kg |
MZ-1200 | DN600–1200 | Φ600–1330 mm | 1150 W | 350 kg |
DN150–250: The M-200 and MZ-250 both reach 600 mm. The MZ-250 weighs 45 kg against 70 kg and covers seats up to Φ270 mm, which makes it the easier machine to carry up scaffolding.
DN200–400: The M-300C is the usual choice, with seats from Φ118 to Φ430 mm. Move to the M-600 only when the seat is larger than Φ430 mm.
DN400–600: If the seat fits the M-600's Φ225–630 mm range, it weighs 80 kg against 270 kg for the MZ-900. The MZ-900 is for seats beyond Φ630 mm or valves that need its 1000 mm reach.
DN600–1200: The MZ-1200 is the machine for extra-large valves. At 350 kg with a 2000 mm reach, plan the lifting and mounting bracket before the shutdown starts.
If your valve sits between two models, send us the drawing and measurements and we will tell you which one to use.
Gate Valve Size Chart: DN, Inch and Model
If your valve is specified in inches, convert it here first.
DN | Inch (NPS) | Candidate Models |
|---|
DN50 | 2 in | MZ-150 |
DN80 | 3 in | MZ-150, M-200 |
DN100 | 4 in | MZ-150, M-200, MZ-250, M-300C |
DN150 | 6 in | MZ-150, M-200, MZ-250, M-300C |
DN200 | 8 in | M-200, MZ-250, M-300C, M-600 |
DN250 | 10 in | MZ-250, M-300C, M-600 |
DN300 | 12 in | M-300C, M-600 |
DN400 | 16 in | M-300C, M-600, MZ-900 |
DN600 | 24 in | M-600, MZ-900, MZ-1200 |
DN900 | 36 in | MZ-900, MZ-1200 |
DN1200 | 48 in | MZ-1200 |
The M series (M-200, M-300C, M-600) uses planetary grinding with gear transmission, and these models are built as split-type portable machines, which suits valves where the opening limits how large the machine can be. The MZ series (MZ-150, MZ-250, MZ-900, MZ-1200) uses chain transmission with adjustable discs, and the larger MZ models add telescopic arms for big valves.
Seat, Disc or Wedge: Know What You Are Grinding
A gate valve has two sealing pairs, and they are repaired differently. The body seats are ground in place, with the machine mounted inside the valve body. The disc or wedge is a separate part, so it needs a fixture to hold it and an abrasive suited to its face. A wedge has angled faces, and the tooling must match the original angle. A parallel gate has two flat faces that must be ground in alignment.
A standard machine does not automatically include the fixtures for both seat and wedge work. Tell us which components you are repairing, and the quotation will list the right tools, which also keeps quotations from different suppliers comparable.
Gate Valve Types and How Each Is Repaired
The valve's construction decides how the seat and disc are handled.
Gate Valve Type | Sealing Geometry | Grinding Approach |
|---|
Solid wedge gate | Angled seat faces, with a wedge cut to the same angle | Grind the seats, then the wedge, so both keep the original angle and mate together |
Flexible wedge gate | Angled faces, with a wedge that can flex slightly | Same approach as the solid wedge; take care not to remove more than needed so the wedge keeps its travel |
Parallel slide or double-disc gate | Flat, parallel seat faces with two discs | Grind both seats flat and in parallel, then grind each disc face flat |
Large-bore gate valve | Same geometries at DN600 and above | Choose a machine with the reach and mounting bracket for the valve, and plan hoisting |
For wedge valves, angle-specific tooling may be needed to match the original seat angle.
Leak Symptoms and What to Do About Them
A gate valve that passes fluid when closed does not always need grinding. This table helps decide before you order equipment.
What You Find | Likely Cause | Is Grinding the Fix? |
|---|
Fine wire-drawing marks across the seat | Throttled flow or slight leakage over time | Yes, usually a quick repair |
Scratches or scoring from debris | Scale, weld spatter or particles caught on closing | Yes, if the scratches are shallow |
Light pitting or corrosion | Chemical or erosion attack on the surface | Depends on the depth; light pitting grinds out |
Deep erosion channels | Sustained high-velocity leakage | Usually not; overlay or seat replacement is needed |
Leak behind the seat ring | A loose or damaged seat ring | No; the ring itself needs attention |
Wedge and seat no longer mate | Wear, heat distortion or uneven grinding | Yes, by grinding seat and wedge as a pair |
Grinding vs. Hand Lapping vs. Overlay vs. Replacement
Option | Where It Fits | Limit |
|---|
Portable machine grinding and lapping | Valves in the line, large valves, short shutdown windows, seats with shallow or moderate damage | Needs seat material left and room to mount the machine |
Hand lapping | Very light wear on small valves | Slow on large seats and can leave the seat out of flat |
Weld overlay and machining | Deep erosion and worn-through hard facing | Needs a welding procedure and finish machining |
Replace the seat ring or the valve | Cracked or loose seats, or damage beyond repair | Highest cost and longest downtime |
A Typical On-Site Gate Valve Repair, Step by Step
Isolate and depressurize the line under your site procedure, then remove the bonnet and gate to expose the seats.
Clean and inspect both seat faces for scoring, pitting and erosion. Measure the seat diameter, the depth to the seat and the opening, and judge how much material can safely come off.
Choose the machine, grinding plate and abrasive from those measurements and the seat material.
Mount and center the machine in the valve body so the grinding plate runs true to the seat.
Grind in stages: a coarser abrasive to remove the damage, then finer grits to finish, ending with lapping where a very fine surface is needed.
Check the contact pattern on the sealing face, and grind or lap the disc or wedge so it mates with the restored seat.
Reassemble and leak-test to the standard that applies to the valve before it returns to service.
On the largest machines, the MZ-900 at 270 kg and the MZ-1200 at 350 kg, mounting is a lifting job, so arrange hoisting and access at the planning stage.
When Grinding Is Not the Answer
Grinding removes material from the seat and the wedge. A light surface repair is exactly what it is good at. It is the wrong tool when damage runs deep: erosion channels, cracks, a seat ring that has loosened in the body, or a hard-facing layer that would be cut through. Those cases need weld overlay or seat replacement. Before grinding, also check that enough seat thickness and stem travel remain to take the material you will remove. We would rather tell you that during selection than sell you a machine for a valve it cannot save.
Grinding Tools, Abrasives & Seat Materials
The abrasive has to suit the seat material, and the grit follows the condition of the surface: coarse to take out damage, fine to finish. Standard models use replaceable grinding plates and abrasives, and grit options such as 80, 120, 220 and 400 are available.
Seat Material | Tooling Direction |
|---|
Carbon steel | Standard abrasive tools matched to the surface condition |
Stainless steel | Abrasive discs suited to the material and required finish |
Hardened steel | Optional hard-material grinding tools |
Stellite-overlay seat | Optional CBN or diamond-based tooling where suitable |
Other hard-faced or coated seats | Special tooling after review of the coating and substrate |
Diamond and CBN tools are options and are not standard on every model.
Custom Gate Valve Grinding Configurations
When a valve falls outside the published ranges, we adapt the tooling around the machine instead of designing a new one:
Valves below DN50 and special projects up to DN1600, designed for the specific job
Special grinding plate diameters, and wedge angles taken from your valve drawing
Extended shafts and special-depth setups, beyond the standard 600, 1000 and 2000 mm reaches of the current models
Custom centering fixtures, clamps and supports for tight or awkward valves
Pneumatic drive, and 110/120 V or 220/230 V supply at 50 or 60 Hz, in place of the standard AC 220 V / 50 Hz
One machine will not cover the whole span from DN15 to DN1600, and each custom project is checked against your confirmed dimensions before we quote.
Portable Gate Valve Grinding Machine FAQs
Which machine suits a DN300 gate valve?
The M-300C is the usual starting point, with a DN100–400 range, Φ118–430 mm grinding diameter and a 55 mm minimum opening. Check your actual seat diameter and the depth to the seat against it, because a DN300 valve can have a different seat size from another maker's DN300.
How deep a scratch on the seat can be ground out?
Light scoring and wire-drawing grind out without trouble. A scratch that is still visible after the surface is cleaned up means the damage runs deep, and removing it may leave the seat too thin or cut through the hard facing. In that case overlay or seat replacement is the better repair.
How do I choose between the M and MZ series?
Fit comes first: the seat diameter must be within the model's range, and the machine must pass through the opening and reach the depth. Where two models both fit, the lighter one is easier to carry and mount. The comparison above shows where the series overlap.
Can one machine grind both the seat and the wedge?
The models are designed for seat and disc maintenance, but the body seat and the removable wedge need different tools and fixtures. Say which parts you repair, and the quotation will list the right accessories.
Can you supply machines for valves larger than DN1200 or smaller than DN50?
Yes, as special projects. The standard MZ-1200 covers DN600–1200 and the MZ-150 covers DN50–150. Larger valves up to DN1600 and smaller valves are reviewed individually, and a standard MZ-1200 should not be assumed to cover them.
What is the difference between grinding and lapping a gate valve seat?
Grinding removes material to correct geometry: flatness, angle and surface damage. Lapping is the final fine finish with a very fine abrasive, and it gives the smooth surface that seals. Most repairs use both, so the quotation lists abrasives for each stage.
Why use a machine instead of lapping by hand?
A machine holds the grinding plane square to the seat axis and applies even pressure, so the seat comes out flat and the result is repeatable. Hand lapping suits light wear on small valves. On large seats it is slow, and it can leave the seat out of flat.
How do I know whether my gate valve needs grinding?
A valve that passes when fully closed, with fine wire-drawing marks or shallow scoring on the seat faces, is a typical candidate. Deep erosion channels, cracks, or a leak behind a loose seat ring are not. The symptom table above sets out the common cases.
How long does a gate valve seat repair take?
It depends on the valve size, how deep the damage is, the seat material, and how much set-up the valve needs. Light wear on a small valve is quick, and a large or hard-faced valve takes longer. We cannot quote a fixed time without knowing the valve.
Which test standard should I use after the repair?
Use the standard that applies to your valve and your customer. General valve leak tests are often specified to API 598 or ISO 5208. Grinding does not replace the test, and the valve should return to service only after it passes.
Request a Gate Valve Grinding Machine Quote
For a recommendation and quotation, send:
Valve type (parallel or wedge gate) and nominal size
Actual seat diameter, wedge dimensions, seat material and which parts you will repair
Depth from the mounting point to the seat, and the smallest opening
Power supply or compressed air, destination country and quantity
A valve drawing or clear photos, if you have them
Request a Quote
