Re: V4 fuel pump diaphragm; supposed to be one spring or two? Home › Forum › Ask A Member › V4 fuel pump diaphragm; supposed to be one spring or two? › Re: V4 fuel pump diaphragm; supposed to be one spring or two? frankrUS Member - 1 Year (includes $3 online payment fee)Replies: 6715Topics: 51 February 4, 2018 at 2:06 am #70583 It indeed takes two springs, different lengths. The upper one in the picture is the chamber that does the actual pumping. The lower chamber is called an air dome, and it’s function is to smooth out the individual pumping pulses.