Come on brains!

[kaboom]

Saw a newly re-located open vented cylinder today with a couple of things I thought odd.
Firstly the feed vent set up was 'H' shaped. The flow came up and became the vent, the feed came down and became the flow. The link (flow) was 150mm and the pump on the exit leg of the 'H'. Isn't this a recipe for sucking air?
Secondly, the coil was fed in 22mm but reduced to 15mm on the return. Any ideas why that would be done?

 

[Slugbabydotcom]

Difficult to interpret without seeing a pic but heres my take on it!
If the feed and vent are on the flow next to each other with the pump on either side you wont get suction or pressure as both the pipes are under near enough the same -ve or+ve pressure. Putting the pump in between feed and vent = probs.

15mm on the return doesnt sound right at all. Who fitted it and where did he park his horse?

PS
Don't know whether I should have answered this as Im recovering from a bout of dyslexia and my name isnt Brian

 

[kaboom]

Sorry if I wasn't too clear. I think its the type of set up where you'd see an air seperator, but there isn't one. Surely the flow will try to go straight up the vent?

Feed x xVent
x x
x 150mm x
xxxxxxxxxxx
x Flow x
Flow x ^Flow
x ^
x ^
Pump
to s plan

 

[kaboom]

AHHHHHHHHHHHHHH! That was a pretty diagram until it posted.

 

[fitz1]

STANDARD PRACTICE IF NOT USING AN AERJEC.FEED AND EXPANSION WITHIN 150MM.15MM RETURN CIRC ON FULLY PUMPED SYSTEM NOT A PROBLEM AND QUIET COMMON. I HAVE SEEN 8MM CICS MANY TIMES AND THEY HAVE WORKED FINE.

 

[kevplumb]

dont shout

 

[ChrisR]

Idea being that if the boiler is boiling, the vapours can go up the vent, and new cool water can come down the feed at the same time.

Careful using "expansion" chaps it's a mistake. The water expands up the feed pipe, not (much) up the vent.

 

[kaboom]

Please don't bite my head off but I blew the dust off of my design guide. It says the feed and vent should come off of a horizontal run where as in this 'H' set up that's obviously not the case. Anyway, having said I'd never seen it done that way what do I find today? Yep, an almost perfect copy. Guide also says pump shouldn't pump down, which they both do. The guide also says the cylinder f & r should be min 22mm. The guide............ is it tosh?

 

[oilman]

Hs are common as are pumps pumping down, as are pumps upstairs without enough head. But then they're put in by qualified plumbers, so what do you expect?

 

[kevplumb]

ooooh bitchy

 

[kaboom]

Not sure if that dig is a for me or for the 'qualified plumbers' Oliman?

 

[kevplumb]

oilman mate
rest easy

 

[kaboom]

Is he telling me what I've seen is bad practice? Perhaps I'm being dense but I really would like to know!

 

[kevplumb]

feed and vent should ideally be "close coupled" ie within 150mm of each other this is not always practical then the thinking cap comes out

 

[oilman]

It's not a dig at anyone in particular, and I don't see any problem with the H connection. F&E and vent are close together to keep the pressure difference between them low, then the vent doesn't spend its life pumping over. The pump facing down is bad practice, as is having not enough head over the pump