Windscreen Washer Advice

[crashbarrier]

To start with I had very little flow from the washers, more a dribble, and I've been doing some investigating. I've replaced the wipers and washer heads as an alternative to the original loop type but instead of a fountain, I'm getting a pathetic attempt to spray. I've finally managed to extricate the reservoir after it resisted all attempts to '"just push up". It's nice and clean inside so no expected sludge build-up and the motor seems to whirr away quite energetically when energised. The washer hose seems to be nice and clear inside when I wipe away the outside crud so I then wondered about the non-return valve.

Non-return valve - It's located just along from the reservoir and when I disconnected it from the upstream hose lots of lovely blue wash fluid flowed out from the hose above which leads me to believe that it's not sealed or partially blocked further up towards the wipers.
I've tried to blow through the valve in the correct direction and it seems to be blocked as there is hardly any flow of air but there is a little.
I've rigged the system up without putting it back in and with the valve removed the flow at the wipers is a bit better but still not great.

Q. Is the valve supposed to be so resistant to being blown through as I can't imagine the pressure from the pump is much? I did a test with a blow pump as well as my lungs but to no avail.

Q. Could I just leave the NRV out of the system? I presume that it prevents the fluid in the hose upstream from slowly feeding back into the reservoir under gravity so it'll mean a wait for the water to flow and some dry wiping.

Q. With valve removed could the pump simply be on its last legs even though it sounds OK and just not producing the pressure needed to re-create the Bellagio fountains?

I'm trying to resist just blindly buying new parts in the hope that I resolve the problem but if the advice is to do so then.

Any advice gratefully accepted.