The MARS 12078 is a round-case design

this relay is a direct replacement part for maintaining system safety and efficiency

Is the 40-inch measurement the internal or external length

As the direct replacement for 2578400 and 2568516

Siemens Building Technology 331-2904 Actuator 321142-301 The MARS 12078 is aThe Siemens 331 2904 is a heavy duty #4 pneumatic damper actuator designed for the gradual or positive actuation of large dampers in commercial ventilating systems. This piston type actuator features an all metal body construction and is specifically UL recognized for high stakes fire and smoke applications. With a 3 7 psi spring range and a generous 4 inch stroke, it provides the necessary force for reliable operation of outdoor air, return air, and