Go on the Mallory web site and read their installation instructions and the tech bulletins for Mallory 140 pump and 4309 bypass style regulator. I thought I could get away with a 1/2" (-8) feed and a 3/8" (-6) return but no way. According to the Mallory tech bulletin with the regulator backed off all the way the back pressure (gage pressure) needs to be 3 psi or less. With the 3/8" return line my back pressure was 6 psi. So I took out the 3/8" (-6) return line and replaced it with a 5/8" (-10) line. Always costs more when you have to do it twice. With the 5/8" (-10) return the back pressure was less than 1 psi. I don't know if the 1/2" line would have worked or not but I didn't want to chance doing the job 3 times. I use the Mallory 140 pump and the 4309 regulator. The Mallory 140 pump comes in two different configurations. If it is used with a dead head regulator it is internally by passed and set from the factory at 12 psi (not sure on pressure). If you use the by pass regulator the pump is not internally by passed. This is all explained in their istallation instructions and tech bulletins on their web site. All good reading and very imformative.
Tim C
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Tim Corcoran
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