ktichen tap - slow start

[patters_uk]

I have a mixer tap in the kitchen and there is a problem in that when I turn on the hot tap (quarter turn valve) there is often up to a 15 second delay before any water comes out. There is no problem with the mains cold and the hot is fed from the cylinder which is upstairs and about 12 feet away although pressure was never brilliant. Pipework downstairs is 22mm feed reducing to 15mm. Hot water is softened. There is a hot feed to the washer from the undersink cupboard but turning that off makes no difference to the delay.

So far I have tried ...
1) A replacement tap (now a Franke mixer) same problem although it didn't do it immediatley.
2) Moving the HW supplied to the 3.5 bar Monsoon pump. Once the water starts and the pump kicks in then it gushes out.

So I am now at a loss .. I'd have thought the overrun on the pump would keep the pressure in the pipe, but it seems not to be the case. the tap can be turned off for just a couple of minutes and when it is turned on again we get the same lag. I can only assume it's a sticky valve but then why has it happened to 2 different taps. Plumber is also confused as to what it might be.

Any advice/observations appreciated

Denis

 

[tamz]

You have bought the wrong taps. High pressure when you should have bought low.

The pressure disappears as soon as the pump stops because the system is open to the atmosphere.

If you had gotten a decent plumber to begin with he would have known this.

 

[patters_uk]

Taps are low pressure monoblock .. Franke Eiger C. Work on 0.39 bar minimum 5 bar max. Also problem was there with or without pump, though has seemingly got worse with pump. True enough it's an open system with the cold water tank in the loft but I don't quite understand why the pressure would drop downstairs unless there was air getting into the system, bu there are no leaks that I am aware of.

 

[tamz]

0.39 bar equates to about 4m head of water. Not exactly low pressure. If your house is a bungalow you are below that. Even a 2 storie will be borderline with pressure losses through pipe.

The hot pipe, through the cylinder is connected to an open vent and also a feed pipe from the cold cistern. Either one will mean the pipe cannot remain pressurised once the pump stops.

 

[patters_uk]

thanks tamz. It is a 2 story house with tank in loft with a fairly direct route to the kitchen tap. Should've tried timing filling a bucket before I had it pumped. Is there any easy way of measuring "ambient" pressure in the pipe. Is it possible to fit a non-return valve betwen the pump and the tap to "retain" the pressure

 

[tamz]

Don't get pressure and flow mixed up. Filling a bucket and timing it would only give an indication of flow rate, not pressure. To test the pressure you need a pressure guage or in the case of cistern fed, measure it from the cistern outlet to the discharge point. (that is about all you really need to know without complicating matters)

Your tap requires a static (standing) pressure of 0.39 bar to act upon it to allow it to open. As the tap will open eventually, it must be near this or would not open at all.