One Way Valves and boiler feed lines

[2xlp]

My Venus is in parts, and my expobar will soon be.

Looking at both, neither have a 'one way valve' leading from the pump to the boiler.

Should they? Regarding the designs on each, isn't the boiler pressure as it heats forcing back on the pump - even when its off? And the pumps are rated for ambient temps , doesn't this heat the pump to some extent?

[chardinej]

My NS Oscar has a tiny one-way valve between the pump and the hot water system. The valve fits inside a brass fitting and you would never know it's there from the outside.

[erics]

The Ulka pump has a check valve built into the discharge port and some OPV's (e.g. Expobar) also have a check valve built into them.

See this: http://www.home-barista.com/forum...ry-pump-t1079.html

Here is a link to a beautiful description of the Expobar OPV as found on the Brewtus: http://tinyurl.com/ykgp4z

I believe this OPV has been improved since Sean L. wrote the above paper and the improvements were described by DaveC here: http://myweb.tiscali.co.uk/coffee...iles/OPV_Valve.pdf

Eric S.