Very Slow Float Valve

[buddha]

I've just installed a new toilet.
All works fine except the float valve (bottom entry) fills very slowly. Takes about 5 minutes.
A small jet/trickle of water exits the small outlet at the top, but not much/nothing exits from the bottom of the valve - which is where I expected the majority of water to exit into the cistern.
The water supply is from a cold water tank with over 2 metres head.
I've also tried removing the small blue plug (on the top) which I think should be in place for high pressure (mains fed) systems - but this doesn't work.
The valve is made by a company called R&T. But cant find anything about them online.
Any advice on what I can do? apart from getting a different one.
Thanks.
Here's a picture of the offending item:

 

[Bas]

if you have read the instructions and your water pressure is within limits I'd throw it away and buy a torbeck valve. They come in two bottom entry sizes - so make sure you get the right one. And flush the pipework before fitting

 

[ChrisR]

Take it to bits and sus out how it works - not always a simple task! There might be a hole somewhere you can drill out a bit, which can make a huge difference.

 

[buddha]

I did the take it to bits - how it works route.
It seems that the valve uses the water pressure passing up its central core to 'lift' a diaphram, allowing water to pass back down an outer sleeve to the base of the valve - into the cistern.
So it would seem that I do not have enough water pressure
As I bought the suite online, I'll have to wait till tomorrow for a reply from the supplier and can hopefully get a'low pressure' replacement.
Thou if anyone else has had a similar problem, I'd be grateful to know their solution.
Thanks for your replies