51.0401.09 InterpumpGroup W1210 Piston D. 18x25 Buyer's Guide: Sizing, Compatibility and Sourcing Worldwide

The 51.0401.09 InterpumpGroup W1210 piston D. 18x25 is a replacement piston assembly for Interpump W-series plunger pumps, specified at 18 mm diameter x 25 mm stroke. Buyers searching this part number are almost always maintaining an existing Interpump pump rather than specifying a new one — so the critical question is not "what does it cost" but "does it fit my pump's crankcase and manifold."

What is the 51.0401.09 Interpump W1210 piston D. 18x25?

A 51.0401.09 InterpumpGroup W1210 piston D. 18x25 is a reciprocating pump piston (plunger) assembly — an 18 mm diameter, 25 mm stroke wear component that pressurises water inside an Interpump W-series pump head. It is a service part, not a standalone pump.

Interpump Group S.p.A. is an Italian manufacturer whose plunger pumps dominate high-pressure cleaning, reverse-osmosis, misting and industrial process duty worldwide. The W-series is one of the group's long-running reciprocating platforms, and the 51.0401.09 piston is one of several diameter variants in that family.

Because the piston is a wear item, it is normally replaced as part of a seal-and-valve service kit rather than in isolation. Buyers who replace only the piston and leave worn seals in place typically see the new piston fail within a few hundred hours.

How does an Interpump W-series piston work?

The piston reciprocates inside a ceramic or hardened-steel liner, drawing water through an inlet valve on the downstroke and forcing it through an outlet valve on the upstroke. Pressure is generated by the restriction downstream — a nozzle, a valve, or a process line.

Piston diameter and stroke together set the pump's displacement per revolution. An 18 mm x 25 mm piston is a mid-range size: larger diameters move more water at lower pressure, smaller diameters reach higher pressure at lower flow. This is why the same W-series crankcase can be built to several pressure/flow ratings simply by changing the piston set.

At 1750 rpm, an 18 mm x 25 mm piston geometry is consistent with the 15 L/min (3.96 US gpm) class of Interpump pump — the same flow band as the Inter[[PRODUCT:TS1331-000|pump TS1331 and the Inter[[PRODUCT:T01321-000|pump T1321.

Spec table: 51.0401.09 piston and matching pump envelope

The table below lists the measurable attributes that matter when matching this piston to a pump. Values are drawn from the Interpump datasheet envelope for this product family.

Note the 50 Hz / 60 Hz distinction: at 1750 rpm the pump is a 50 Hz, 4-pole machine. On a 60 Hz supply the same pump runs at approximately 3450 rpm, which raises flow by roughly 20% and absorbed power by roughly 70%. Always confirm the motor frequency before ordering a piston set, because the correct piston diameter depends on the target duty point, not on the nameplate alone.

Which Interpump pump models use this piston class?

The 18 mm x 25 mm piston geometry sits in the mid-range of the Interpump W-series and is shared across several pump families that differ mainly in manifold, valve and drive configuration. Buyers should match on three things: piston diameter, stroke, and crankcase series.

• Direct-coupled industrial pumps — flange-mounted to a standard electric motor, the most common configuration in cleaning and process duty.
• PTO-driven pumps — belt or shaft driven from a tractor or vehicle engine, common in agricultural spraying and mobile washdown.
• Bare-shaft pumps — supplied without motor for OEM integration into a larger machine.

If you are replacing a piston rather than specifying a new pump, the fastest route is to read the pump nameplate and cross-reference the piston diameter stamped on the manifold. Interpump stamps the piston size on the pump body on most W-series units.

Selection criteria: how to choose the right piston and pump

1. Confirm piston diameter and stroke. An 18 mm x 25 mm piston will not fit a crankcase machined for a 20 mm or 16 mm plunger. Measure or read the stamp — do not assume from the pump model alone.
2. Match the pressure/flow duty point. If your process needs 200 bar (20 MPa / 2,900 psi) at 15 L/min (3.96 US gpm), the 18 mm piston is correct. Higher pressure needs a smaller piston; higher flow needs a larger one.
3. Check the drive frequency. A 50 Hz supply gives 1750 rpm; a 60 Hz supply gives roughly 3450 rpm on the same 4-pole motor. Recalculate flow and power before ordering.
4. Assess water quality and duty cycle. Abrasive or high-temperature water shortens piston and seal life. Continuous duty (24/7) needs a shorter service interval than intermittent cleaning duty.
5. Replace seals and valves at the same time. A piston fitted into a worn seal set will fail early. Budget for a full service kit, not a single part.
6. Verify the coupling and flange. If you are replacing a pump rather than a piston, confirm shaft, flange and coupling compatibility — see the Interpump Flexible Coupling 56C for a common 56C frame match.

Product selection ladder: Interpump pumps and accessories from 3G Electric

The table below arranges representative Interpump products from light-duty accessory through to heavy-duty industrial pump, so buyers can see where the 18 mm piston class sits in the range.

Step up the ladder when your duty point moves beyond the 15 L/min (3.96 US gpm) / 200 bar (20 MPa) band — for example, moving from intermittent cleaning to continuous process duty, or from a 5.73 kW (7.8 hp) drive to a 15.44 kW (21 hp) drive. The Interpump T2830Y SX with 53R geared motor is the flagship in this comparison, delivering 30 L/min at 275 bar (27.5 MPa / 4,000 psi).

Why source the 51.0401.09 piston and Interpump pumps from 3G Electric?

3G Electric stocks 4,007 products across 14 industrial departments — machining, electrical, power transmission, material handling, plumbing, HVAC and refrigeration, pneumatics, hydraulics, pumps, instrumentation, test and measurement, welding, lighting, and combustion/burner systems. Pumps, combustion and controls are our deepest specialist areas, but they are not the limit of what we supply.

With 35+ years of experience interpreting customer demand, we do not simply ship a part number — we confirm the piston diameter, stroke, drive frequency and duty point against your pump before quoting. For Worldwide buyers we supply incoterms-neutral, with export documentation experience across multiple markets and both 50 Hz and 60 Hz motor variants available on request.

We are a distributor and supplier of Interpump products, alongside brands such as Schneider, ABB, Siemens, SKF, Festo and Fluke. We are not an authorised dealer for every brand we carry, and we will tell you plainly when a part is out of production or superseded.

According to the Interpump Group S.p.A. datasheet SS3C2015 (dated 3/21/2026): "Male shaft (key) - (plugs) - OUT OF PRODUCTION."

That note is a reminder that Interpump's W-series has been revised over time. Some shaft and plug configurations are no longer produced, and the correct replacement may be a superseded part number. Always confirm availability before committing to a maintenance schedule.

Frequently asked questions

What is the 51.0401.09 InterpumpGroup W1210 piston D. 18x25 used for?

It is a replacement piston for Interpump W-series plunger pumps, used in high-pressure cleaning, reverse-osmosis, misting and industrial process duty. The 18 mm x 25 mm geometry suits pumps rated around 200 bar (20 MPa / 2,900 psi) and 15 L/min (3.96 US gpm) at 1750 rpm.

How do I know if an 18 mm x 25 mm piston fits my pump?

Check the piston diameter stamped on the pump manifold and the stroke specified in your pump manual. An 18 mm piston will not fit a crankcase machined for 16 mm or 20 mm plungers. If the stamp is unreadable, measure the plunger OD with a micrometer.

Should I replace the piston alone or as part of a service kit?

Replace it as part of a full seal-and-valve service kit. A new piston running against worn seals or scored valves will fail within a few hundred hours. Budget for the kit, not the single part, and inspect the liner at the same time.

What is the lead time for Interpump parts delivered Worldwide?

Lead time depends on stock status and destination. In-stock items typically ship within days; out-of-production or superseded parts require a sourcing check. 3G Electric supplies incoterms-neutral with export documentation, so confirm your preferred Incoterm and destination port at quote stage.

Does the piston differ between 50 Hz and 60 Hz supplies?

The piston itself does not change, but the duty point does. A 50 Hz supply runs the pump at 1750 rpm; a 60 Hz supply runs it at roughly 3450 rpm, raising flow by about 20% and absorbed power by about 70%. Confirm frequency before ordering.

Where can I buy the 51.0401.09 piston and matching Interpump pumps?

3G Electric supplies Interpump pistons, pumps and accessories worldwide, with technical support to confirm compatibility before you order. Contact us with your pump nameplate details and duty point for a quote.

Key takeaways

• The 51.0401.09 InterpumpGroup W1210 piston D. 18x25 is an 18 mm x 25 mm wear part for Interpump W-series pumps, rated around 200 bar (20 MPa / 2,900 psi) and 15 L/min (3.96 US gpm) at 1750 rpm.
• Match on piston diameter, stroke and crankcase series — never on pump model name alone.
• Replace seals and valves with the piston; a lone piston in a worn head fails early.
• Confirm 50 Hz vs 60 Hz before ordering, because flow and power change materially.
• 3G Electric stocks 4,007 products across 14 departments and supplies Worldwide with export documentation and technical sizing support.

Ready to order or need a compatibility check? Contact 3G Electric with your pump nameplate, piston diameter and duty point. We will confirm the correct part, quote in USD, and advise on lead time and export documentation for your market.