Stokes Vacuum Pump Spare Parts

Yes — extensively. Although Stokes is now operated as a brand within Edwards Vacuum (Atlas Copco), the Microvac rotary piston pumps remain in production and we hold dedicated UK stock for the 212H-11, 212J, 412H-11, 412J, 612J, 149H-11, and 148H-13 frames. Spares include hinge bars, piston ring sets, exhaust valves, shaft seals, gaskets, bearings, and complete rebuild kits.

Hinge bar wear is the most common failure on rotary piston pumps — the floating hinge bar that guides the piston eventually wears, increasing piston-to-cylinder clearance and reducing pumping capacity. Piston ring wear is the next most common, typically appearing at 10,000+ running hours. Both are addressed with our standard rebuild kits.

A Microvac uses a piston driven by an eccentric crankshaft, sealed by piston rings, with hinged guide bars — quite different from rotary vane technology. The piston design tolerates particulates, condensable vapours, and process water vapour far better than rotary vane pumps, making Microvacs the industry standard for dirty heat-treat, metallurgy, and transformer-drying duty where vane pumps would fail rapidly.

Yes. Major rebuild kits for the 412H-11 / 412J include hinge bars, piston rings, piston assemblies, exhaust valve plates and springs, shaft seals, bearings, and a full gasket set — everything needed for a complete pump overhaul. Minor kits (rings + valves + gaskets only) are also available for routine service.

Oil emulsification — the cloudy, milky appearance of contaminated oil — is caused by water vapour ingress, typically from quench loads in heat-treat or moist process gas. Per Stokes' service guidance, run the pump with the gas ballast valve open during high-vapour duty cycles to purge the water vapour from the pump. Once emulsified, oil must be drained, the pump flushed, and fresh oil added.

Some are, some aren't. Following the Edwards acquisition, Stokes Microvac models were given Edwards-Stokes part numbers — the wear parts (hinge bars, rings, valves) are largely common between original Stokes part numbers and current Edwards-Stokes designations. Our team can cross-reference between original Stokes, Pennwalt-era Stokes, and current Edwards-Stokes part numbers to identify the correct replacement.

Microvacs are renowned for longevity — many are still in service after 30–50 years with periodic rebuilds. Major rebuild interval is typically every 5–10 years depending on duty cycle. With clean duty (e.g. high-vacuum freeze drying), intervals are even longer; with dirty heat-treat or metallurgy duty, shorter. The investment in a major rebuild kit is almost always far less than a replacement pump.

Common in-stock items (hinge bars, piston ring kits, gasket sets, exhaust valves for 212H-11 and 412H-11) are available on a next-day UK mainland basis. Some specialist or rare components (older 1722 booster spares, NOS items) may require additional lead time — we'll confirm availability and timeframe at the point of enquiry.