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Mike Noc · 21st March 2012, 06:52

They are different designs - as you say the UBP is a type of screw pump but the ITP has a rotary impeller.

The ITP is self priming due to a normally open ball valve situated at the top of the pump, allowing diesel to flow in. This closes as the pump pressure builds up.

This means that with a failed ITP the ball valve is open so the UBP doesn't actually have to suck fuel through the ITP itself. It also means that when the fuel level drops down below the top of the ITP the UBP will start sucking air. Another clue to why the car can stop with a quarter tank of fuel onboard after the ITP has packed up.

Mike

21st March 2012, 06:52	#7
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,549 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	They are different designs - as you say the UBP is a type of screw pump but the ITP has a rotary impeller. The ITP is self priming due to a normally open ball valve situated at the top of the pump, allowing diesel to flow in. This closes as the pump pressure builds up. This means that with a failed ITP the ball valve is open so the UBP doesn't actually have to suck fuel through the ITP itself. It also means that when the fuel level drops down below the top of the ITP the UBP will start sucking air. Another clue to why the car can stop with a quarter tank of fuel onboard after the ITP has packed up. Mike Last edited by Mike Noc; 21st March 2012 at 07:01..