LPowners.org Safety valves

by Bruce Colglazier Pappas

There have been many safety valve changes over the years. Here is what I have discovered. [Thanks to Stefano's site for this info.]

P37 - body

P37
Gen1 (vintage) & Gen2 (PreMill). The first safety valve featured a body with a 5mm hole and a stainless steel ball and spring.

First SS ball & spring

P37
Gen1 (vintage). This is the SS ball & spring in the first safety valve (no longer available).

P39SE - Teflon ball & spring

P39SE
Gen2 (PreMill). The SS ball and spring were replaced by a Teflon ball and spring.

P39SP - new Teflon ball & spring

P39SP
Later Gen2 (Premil) with pressurestats. These machines got a different spring (same Teflon ball). The spring had fewer coils compared to the P39SE (above) that it replaced.

MP37 - new body

MP37
Gen3 (Millennium) and Gen4 (Stradivari). LP moved to a new valve body with a 6.5mm hole to accomodate a new safety valve with anti-vacuum. Here's an explanation of the difference between the two safety valve assemblies: PDF from Stefano.

MP39SP-SE - new valve with anti-vacuum

MP39SP-SE
Gen3 (Millennium) and Gen4 (Stradivari). LP also moved to a new safety valve, which added an anti-vacuum feature.

NOTES:

  • Cap removal: To remove the safety valve cap, you need (1) a thin 16mm open-ended wrench to hold the valve body (to fit under the drain tube) and (2) a 16mm socket & handle to turn the safety valve cap (on top). DO NOT TRY TO HOLD THE VALVE BODY WITH THE DRAIN TUBE, AS IT WILL EASILY BREAK.
  • Body removal: To remove the safety valve body (full assembly), you need (1) a 16mm socket & handle to turn the valve body and a (2) a special close-ended wrench to hold the nut inside the boiler. Some owners have used a flexible T-handle 16mm socket wrench.
  • Anti-vacuum: The MP39SP-SE also includes an anti-vacuum; it is on the top of the valve.
  • Retrofit: You can retrofit the new anti-vacuum valve (MP39SP-SE). If you have a newer valve body with a 6.5mm hole (MP37), you simply replace the valve. If you have an older valve body with a 5mm hole (P37), you need to replace it with a new one (MP37), too.
  • "Lever erectus": This appears to explain why some machines have "lever erectus" (those with old valves) and others don't (those with new valves due to the anti-vacuum). "Lever erectus" is where the lever spontaneously moves to its top position as the boiler cools down.
  • Timeline? Is this timeline for safety valve changes correct?

Created 17-JAN-2018 | updated 06-FEB-2023 | BCP