Flow rate with Grohe Euro fittings?

[daveth]

The flow rate from my cheap n cheerful unbranded 'Chinese' monobloc mixer tap was worse than the old tap it replaced. I decided to upgrade to a Grohe unit (assuming it would be good gear as they are a premium brand) and thought about changing the mini isolating valves to proper lever type cut off valves to improve the flow.

I purchased a Grohe 'Concetto' tap online and was surprised to find it arrived with 'euro' sized 3/8 fittings, so the the job is now stopped whilst I source some adapters. :veryangry2:

Having looked at the flexis on the tap, the internal bore is a meagre 4.5mm compared to the internal bore on my std feed pipes of 13mm. These flexis are not removable, so I cant simply upgrade to wider flexis with 1/2 fittings.

Being a total noobie, I would like to know:
1) Will Grohes 3/8 flexis kill the flow rate?
2) The tap is specced at 13L flow a minute at 3 bar. Is that good/bad/indifferent?
3) Given the small bore flexis is there any point in upgrading mini isolating valves to a lever valve?

Thanks for any input!

 

[SimonG]

How you providing hot water? Combi, unvented cylinder or vented cylinder?

 

[Howsie]

If that's a basin tap then why would you possibly want it to flow at 13l/m? Do you have a mains pressure system or gravity? To me it sounds like you may have fitted a high pressure tap to a low pressure set up.

 

[Phil]

If you fit that tap to a vented cylinder in an upstairs bathroom the hot flow will be so low you could hold a lighted match under the tap and it wouldn't even put it out.

It would take a full day to fill an egg cup.

 

[daveth]

Thanks for the replies

Its in the kitchen in an 'old school' gravity fed vented system - 3 storey house, so good head of water. Hot & cold flow were excellent with the original 1970s tap, just poor with the unbranded cheap tap.

I scooped on the Grohe tap without considering flow rates. I (perhaps wrongly) assumed that my problem was a cheap tap and a decent quality branded tap would rectify the flow. It wasnt described as a high or low pressure tap (some others were). Its flow pressure is stated as 0.5 to 5 bar. Is that good or bad? Sorry total noobie here!

Its not like Im trying to fill a bath with it, but as Phil states I dont want to fit a tap that

would take a full day to fill an egg cup.

:smiley2:

Anyway Ive not even fitted the beast yet, so it might be returnable if the tap spec is an issue.

I just thought the Grohe flexis looked really restrictive and wanted that confirming.

Cheers

 

[Howsie]

You have the wrong tap. You need a low pressure tap and you have a high pressure tap. That is your problem. Easy mistake to make.

 

[daveth]

You have the wrong tap. You need a low pressure tap and you have a high pressure tap.

OK many thanks Howsie, good advice.

Grohes low pressure taps were silly money, but a quick google of Bristans specified 'low pressure' products shows tremendous variance in flow:
Bristan JSFSNKC = 4.7L/min at 0.2 bar, 16L/min at 2 bar
Bristan Vegas = 6.3L/min at 0.5 bar, 16.2L/min at 3 bar
Bristan JSNKC = 7L/min at 0.2, 27L/min at 2 bar

I guess the higher the flow the better, but as this is a kitchen sink not a bath filler, some of these low pressure units have similar flow to my grohe high pressure unit

16L/min seems a a fair flow to me but then again my Grohe unit will flow 10L/min at 2 bar. What is considered good flow?

By my reckoning my cold tank is at least 10 metres up in the loft so i must have 1 bar pressure? Is that right?

Finally do I need a check valve incase of hot/cold pressure difference?

Thanks again for any input. I never guessed a tap could be so involved!

 

[happyflyer]

You have the wrong tap. You need a low pressure tap and you have a high pressure tap. That is your problem. Easy mistake to make.

Howsie is right, we can all make this mistake, some of these fancy taps even have very long flexible hoses with very small diameters, this adds further pressure drop and lowers the flow rate, if you are also getting close to the cold feed tank you are lowering the available head, if you go pressurised your option are opened up to you, better showers, better flow rates etc, watch it with a 3 floors house on a combi if you have outlet on the upper floor and the incomer size???

 

[daveth]

Thanks for the replies

OK the Grohe unit is now returned and fast flowing unit sourced

happyflyer - ive deliberately avoided going the combi route due to the size of the house. To be honest, the water pressure (hot and cold) has always been fantastic, until new fittings were used. Im still not sure how much is down to those crappy isolation valves and how much is down to poor quality taps. im not a plumber as you can tell, but as with so many things, modern stuff seems to be designed to look pretty but has no quality and needs replacing in a few years time.

Anyway hoping this will sort the job!

 

[happyflyer]

All these things like ballofix valves, flexible hoses, new easy action taps, they all have pressure drops that are undesirable.

When I severed my time the plumber I worked with would not let you use a pipe cutter, junior hacksaw and two files, round and flat, a tube cutter reduces the diameter, and old plumbers new and most stuff was tank fed.

All we do now is rely on booster pumps and combi boilers, don't get me on that combi boiler job, my pet hate, like working on the engine of an old mini.

 

[Bob275]

Hello Daveth and all - I'm new to this forum and found this as I have exactly the same issue. We brought a Grohe mono tap for a bathroom sink. It was listed 'for high and low pressure systems' but when fitted in out upstairs bathroom the flow of the hot water (tank is on same floor) is pitiful. We're really quite angry as the tap we had (£50 ish from B&Q) was okay - it just decided to leak after 12 years (how dare it).
Do you guys think I would have cause to return it (same store as above) as not fit for use? It has been fitted for a week now but is not any good.

 

[ShaunCorbs]

You can try but they will probably say your should of check the min pressure info on the box etc

 

[Bob275]

Hi Shaun, I didn't know if I had a high or low pressure system so I brought a tap listed suitable for both - did I do wrong? Is it not as simple as that? I was going to swap it this weekend if possible.

 

[ShaunCorbs]

Hi Shaun, I didn't know if I had a high or low pressure system so I brought a tap listed suitable for both - did I do wrong? Is it not as simple as that? I was going to swap it this weekend if possible.

You have a low pressure system

Low pressure = plastic tank in loft copper cylinder

High pressure = combi boiler or mains pressure unvented cylinder

Normally the dual system taps arnt very good for low pressure, your best getting a tap for low pressure

 

[Bob275]

Thank you for the info, I did suspect a low system as the pressure was never fantastic.
Are you suggesting two separate taps? if so we'd need a new sink with two holes.
I'll take a gamble and exchange (if possible) for a normal 15mm tail tap, the last one wasn't too bad.

 

[ShaunCorbs]

Thank you for the info, I did suspect a low system as the pressure was never fantastic.
Are you suggesting two separate taps? if so we'd need a new sink with two holes.
I'll take a gamble and exchange (if possible) for a normal 15mm tail tap, the last one wasn't too bad.

No just one that is designed for less than 0.1 of a bar (eg low pressure)

 

[Ric2013]

If the OP has 10m head (must be a tall house!), then he'll have 1 Bar, but that's standing pressure. I would imagine the pressures quoted in specs are working pressures i.e. there will be some restrictions in the pipework that will lower the pressure actually available. Isolators should be full bore e.g. Pegler 'Tee ball' valves.
The Grohe pressures listed aren't comparible one with another because some are flow rates at .5 Bar and others are at .2 Bar. If you have a tank-fed system, I'd be inclined to steer away from anything rated at 0.5 Bar. Luddite that I am, I'd go for old fashioned taps with BS1010 or BS5412 workings, but these are rubber-washer type taps that have now largely fallen out of fashion, so you probably won't want them.

 

[Bob275]

Hi all, I'm looking for a replacement to the Grohe Cosmo I have and could do with some advice. I was thinking looking at the thread that I need a low pressure tap with a high flow rate..?
I'm looking at low pressure taps but the flow rate varies from 4 Lt/min (Ideal std Opus) to 21.1 (Homebase Estilo).
Do I just get the tap with the better flow rate?
(Tank is on 1st floor as is the bathroom)

 

[Bob275]

Just to up date on this. I purchased a Estilo Ikon from Homebase at the weekend that had the flow rate as above of 21.1 l/min. This works much, much better. Even with the set up I have there is still a decent hot water flow.

 

[Ric2013]

Good news, and thanks for coming back to us!