Bendix 277340X TR-2 Inversion Valve

Product Description

  • Manufacturer: Bendix
  • Part Number: 277340X
  • Condition: Remanufactured
  • Bendix reman valves have the same warranty as new valves
  • Supply: 1/4″ NPT
  • Delivery (2): 1/4″ NPT
  • Control: 1/4″ NPT
  • Mounting Thread: 1-1/4″-12
  • Width: 1-1/2″
  • Height: 4-5/8″

Inversion valves are air operated control valves, and unlike most control valves are normally open, ie; without control pressure the supply is common to the delivery. The inversion valve is closed by using air pressure from another source and is primarily used in emergency or parking brake systems which operate with air from an isolated reservoir. The valve is also used in interlocking and sequencing applications, where the operation of components must take place in specific sequence.

The TR-2 was designed primarily for use in early DD-3 Safety Actuator installations. It is equipped with a threaded body and nut for mounting.

Cross References: 277340, 277340N, 276854, 811162, 5959931, 6120801, 280092, 285546, 950474, 120302, 3S4904, 6D0917, D2X2031, 2159505, 2508833, CPR100168, 3850364, E3850364, 34651, 182979, 11269501, 141269501, 101747, 3850364, 18A0246, C3TS2A622A, C9HS2B139A, 86683289, 30312335, 20QE1149, 20QE19328, 277340B1, BAR277340, ZAC277340, 12895F1, 36652, 53101208, 53101308, 1362196, 335331, 9335331, 640442, S-11504, 3850364, 25AA0680, 335331, 1200952
A cross reference listing means that this valve is a suitable replacement for the part numbers listed. Some changes in air line plumbing may be required.

With these fundamentals, you will better understand this valve and how it is used in the brake system.


The inversion valve has four basic ports:

  1. Supply port, which is a source of air pressure for the valve.
  2. Delivery port, which is where the air pressure from the supply will be sent to apply the component.
  3. Control port, which is where we control the valve with or without air pressure.
  4. Exhaust port, which is where the air will go to the atmosphere to relieve component pressure that was being applied.

Unlike most valves of its type, the DD-3 inversion valve is normally an open valve, which means that, without pressure to the control port, in its normal state, the air pressure to the supply port will be directed to the delivery port. In other words, air will flow right through the valve.


Introducing pressure to the control port shuts off the supply pressure and connects the delivery port to the atmosphere through the exhaust port, removing the air pressure to the applied component.


The DD-3 braking system uses two inversion valves.

The one located in the rear of the coach is used for the park brake system. The one located in the front spare-tire compartment is used during brake applications when primary air reservoir pressure drops below 45 psi.

In the park brake system, 85 psi regulated air pressure is introduced to the supply port. With the park brake applied (push/pull valve pulled out), we have removed the air pressure to the control port, and supply air goes through the valve, out the delivery port, through the double check valve and to the park diaphragm of the brake chamber, applying our brakes.

With the park brake released (push/pull valve pushed in), we are sending air pressure to the control port, which shuts off the supply air and connects the delivery port to the exhaust port, allowing air pressure from the brake chamber to flow back through the double check valve, to the delivery port, through to the exhaust port to escape to atmosphere. This control port pressure from the push/pull valve is also sent to the lock port on the brake chamber to remove the mechanical lock holding the pushrod in the applied position.

The second inversion valve is a safety feature built into the coach brake system. If there’s a loss of primary (rear) brake air pressure while the coach is moving, this second inversion valve will direct secondary (front) brake application pressure to the park-brake portion of the DD-3 brake chambers so the drive brakes will still function even though there’s no rear brake air pressure.

Air pressure from the primary brake tank is directed to the Control Port of the inversion valve, disconnecting the supply and delivery ports. If that tank pressure is less than 45 psi, the inversion valve opens, allowing secondary application pressure, attached to the supply port, to the delivery port and on to the park brake portion of the DD-3 brake chambers


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