Grundfos 15/60 Pumping Downwards

[rojaca]

grundfoss state that this is a non prefered option and should only be done if there is a suitable means of venting air directly before the pump. The reason being that owing to the design of the pump body, air can become trapped.
Ideally the feed/vent wants to be on a horizontal piece of pipework prior to the pump, the horizontal pipework preferably in a larger diameter. Usually you will find that it goes straight up from the floor and the tee to the pump goes horizontally from it. Not the best as this reduces the likelihood of the air seperating from the water and being vented.
Another option is if an air separator (aerject etc) has been used. This are usually about the size of a small can of beans and in your case will have three pipes going from it. Again this slows up the velocity of the water and allows air to seperate more effectively.
Having said all of this if you've got 20 yrs from your previous pump I don't think you've got too much too worry about

 

[Andygasman2010]

If you're worried about cavitation and the pump is at the top of the system pointing pointing downwards, try lowering the pump speed to 2 or even 1 if you can get away with it. As already said, 1.4m is the minimum head of water required and it's often not achieved with that kind of set up.

 

[iwbnwif]

Yep, have got the required distance to the F&E tank (about 1.6m)

Anyway replaced the pump, everything went smoothly until reconnecting the top valve which now leaks like a sieve. Seems the water is coming out of the valve itself control itself not the compression joint or the joint with the pump. I guess an internal seal has perished so need to replace the whole lot (and there was me thinking i wouldn't need to drain the system again).

As luck would have it the plumbers merchant shuts at 12, so its either Screwfix or Wickes. I read somewhere that you shouldnt use screwdriver type valves, so I plan on a Screwfix gate valve if they have it in stock.

 

[Andygasman2010]

You'll probably be able to fix the leak with some PTFE tape.

 

[oilhead]

Loosen the stuffing gland nut a couple of turns, wrap the exposed thread with PTFE tape and tighten back down. May cure the leak.

 

[iwbnwif]

Unfortunately the valve didn't have a gland nut just some sort of spigot which turned the ball inside.

In the end I got a Flowflex one from Screwfix which is almost identical to the old one but 5mm longer which made it a tight squeeze as there isn't much give in the pipework.

(Fingers crossed) its all working beautifully. Thanks everyone for the advice and tips.