My recollection of typical SU electric fuel pumps found on BL products in the post war period was such that they operated essentially as a lift pump. For this reason they were usually mounted on the engine bay bulkhead above carb(s) with little more than gravity feed to them boosted only by the diaphragm spring. I have seen 1.5 psi mentioned though.
There must have been variants to the design of these long suck, short blow devices though. I remember re-plumbing the double ended SU pump on a Jag XJ12 at 2am on the hard shoulder of M4 many years ago when one side failed leaving me with a dry tank and 10 gallons of fuel in second that otherwise could not reach the engine. Here the pump was under the boot floor adjacent to tanks, so short suck, long blow
