Curious about Drayton zone valve design

[CouchPlato]

Can anyone please help my idle curiosity?

In the diagram attached from the Drayton documentation the valve is closed when the paddle is in the A position.
Would it not be better for the paddle to be in the B position (when closed) so that any pressure from upstream helps to keep the valve shut?
I'm particularly thinking of a scenario where you have pump over-run after the boiler has switched off.

Many thanks!

 

[CountryFan]

Would it not be better for the paddle to be in the B position (when closed) so that any pressure from upstream helps to keep the valve shut?

No and they’ve been like this for years

I'm particularly thinking of a scenario where you have pump over-run after the boiler has switched off.

That’s what a bypass is for

 

[RandomGrinch]

Would it not be better for the paddle to be in the B position (when closed) so that any pressure from upstream helps to keep the valve shut?

I believe it's to do with the capabilities of the motor.
The valve is sprung to the closed position.
If the closed position was in position B, the motor would have to fight not only the spring resistance, but also the flow pressure.
With the closed position in position A, the motor has a reduced working load, as the spring resistance is reduced due to the assistance of the flow.

 

[CountryFan]

I believe it's to do with the capabilities of the motor.
The valve is sprung to the closed position.
If the closed position was in position B, the motor would have to fight not only the spring resistance, but also the flow pressure.

Yes and if fitted that way banging noises can occur