Need help identifying pump ports (picture included)

Hello, I have a new to me Simpson belt drive 4200 machine. I need help identifying what the two ports on the far right are. I would have thought one is a bypass to run to a buffer tank but I am not sure which either of these are. One is stamped OUT (the top port) and IN. The IN port has a plastic plug and the OUT has a brass plug.

Ultimately I am just trying to determine which one to use as a bypass.


It’s stamped in the pump. IN and OUT. They’re giving you the option to have your suction and pressure inlet/outlet on either the left or the right.

So to be sure I understand, they are just redundant ports for the water feed and high pressure line? Do you see any potential ports for the bypass ? Thanks!

Correct. Bypass should be directed to buffer tank if you have one. If not, they sell a T-shape piping to have it directed to your pre-plumbed inlet. Highly recommend getting a buffer tank though. Does not have to be big if it’s a small unit like 4 gpm.

If no buffer tank you could run bypass line out to the ground

Bypass back to buffer is off your unloader and it appears you have a built in unloader. Tak a pic of that. You probably aren’t gonna like the answer your seeking.

Built in unloader, is a built in bypass.

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I’m a few days late on this one but you should be able to plug the port on the unloader and use the other side as your “out”. You’ll have to purchase a separate unloader, unloader block, and whip line. You can then have an unloader with a bypass. Most pumps with a built in unloader don’t give you an alternate “out” option so I’m surprised it has a plug there.

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