What's the difference between H-series and J-series Stokes pumps?

The primary difference is the valve deck design. Stokes H-series pumps (212H, 412H, 612MB) use a poppet-valve deck, while J-series pumps (212J, 412J) use a clapper-valve deck. The two are not interchangeable — rebuild kits, valve components, and some internal parts are specific to each series. When ordering parts or a rebuild kit, the H vs. J designation matters more than the CFM rating, because the valve deck style determines which kit fits.

H-Series Pumps: Poppet-Valve Deck

H-series Stokes pumps — the 212H, 412H, and 612MB — use a poppet-valve deck. Poppets are spring-loaded valves that open and close with each piston stroke. H-series rebuild kits include poppets, poppet springs, and the associated gaskets and seals. These pumps are extremely common in heat treating, coating, and industrial vacuum applications and represent a large portion of the pumps GLV rebuilds.

J-Series Pumps: Clapper-Valve Deck

J-series Stokes pumps — the 212J and 412J — use a clapper-valve deck. Clappers are flat, flexible valve elements that flex open and closed with each stroke. J-series rebuild kits include zytel clappers, clapper springs, and the associated gaskets. J-series kits are not interchangeable with H-series kits, even for pumps of the same CFM rating.

Why the Designation Matters When Ordering Parts

A 212H and a 212J are both roughly the same displacement, but they require completely different valve components. Ordering the wrong kit is a common and costly mistake. Always confirm your pump's full model designation — including the H or J suffix — before ordering. If you're unsure, check the nameplate or call us at (888) 633-7127 with your serial number and we'll confirm the right kit.

Quick Reference

For parts (not kits), see our 212 parts, 412 parts, 212J parts, and 412J parts collections.

For general questions about GLV, see our main FAQ.

Last updated: April 2026

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