How does this work?

[mk2phil]

I have a vented gravity system with a shower pump used to send the water to the show and bath taps in the bathroom. When the pump starts to pump , is its flow/pressure rate limited to how quickly the tank can fill with cold water from the cold water tank in the loft?

Or does it effectively 'suck' the water out of the tank in the loft down through to the HW tank to fill it at the same rate as its pumping?

I only ask becuase after a while of using our shower, the hot water pressure drops right off and I was wondering if the cold waer tank in the loft wasn't filling the HW tank as quickly as it was needed to give the shower a decent pressure?

The tank in the loft is huge and the HW tank is also a larger version.

Thanks in advance.

 

[ChrisR]

It's easier for you to look in your loft tank than it is for us
The supply pipes to the pump should be "adequately sized", but WHERE they're connected ia more important , see your other post.

Yes, pumps have a pressure differential across them. In other words, they suck and blow at the same time.