An influent 60" diameter emergency force main that operates at 28 psi for a wastewater treatment plant.  40 psi is the specified operating pressure.  It will tie in to a 60" section of an existing force main.
A 60X60 tee will be installed where the new line will be connected.  The present consideration is to install gate valves at the upstream side of the mainstream section of the tee and at the tee.  Plug and ball valves are being considered.
I am working on a project right now that has 60" gate valves, 60" knife gates, 48" ball, 54" gate, and 66" gates. American R&D makes gates from 2" up to 84". As for the influent trash and such, they add flush connections that can be automatically turned on so the gate has a full seat. APCO makes ball valves in large sizes but their track record on delivery is spotty at best.
I can tell you that ordering a special 3way valve in 60" will cost a lot more that a gate and a T. Not sure who you have your pipe from, but American Cast Iron got us our 64" T's pretty fast.
Also, from the description you gave I am getting the impresion that the line is not used very often. Have you considered using a rotary check valve? You can set the opening pressure and the cost would be less because there are a lot fewer controls.

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