Well I need to know what is this? I think it is part of the cruise system. Cruise and air throttle both work fine. Air gauge cycles between 110 and 120 psi. White needle effected the most. I know the when I stop the engine air to leaking/sucking around the head of the item in the pic.
Thanks for all the help, you people are GREAT.
Pat,
That is the Bendix RV-1 Reducing Valve. It regulates the input air pressure supplying the Bendix CA-1 Control Module + solenoids. See the cruise control + throttle diagram below. The document linked below explains the function of the RV-1, plus operating and leakage tests. If you decide to replace it, do a Google search to find the best price.
http://www.jackdanmayer.com/Files/Bendix%20RV-1%20Reducing%20Valve.pdf
On a separate subject, if your system air pressure normally cycles between a low of 110 and a high of 120, then your D2 governor is not operating correctly, and you are working your air compressor more than necessary. You should be seeing a difference of about 30 psi between engine air compressor cut-in and cut-out. Should be more like 90-120 psi. You might want to try replacing the D2 and see it helps this situation.
Haldex D2 Governor Service Data (http://beamalarm.com/Documents/haldex_d2_governor_service_data.html)