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| Re: controller Re: LIRR MP-54 #1149 and its ME-23 brake valve (485814) | |||
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Re: controller Re: LIRR MP-54 #1149 and its ME-23 brake valve |
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Posted by Jeff H. on Tue Sep 4 19:35:03 2007, in response to Re: controller Re: LIRR MP-54 #1149 and its ME-23 brake valve, posted by randyo on Tue Sep 4 15:21:21 2007. That latch is quite an enigma. I have never been able to finda WABCO piece number or designation on it. I traced back the pattern number on one of the castings and it was evidently a kit-bash of several WABCO parts designed for another purpose, all of 1920s vintage. The design is defective from a pneumatic standpoint. There are two ball poppet valves. One is designed normally in that there is always brake pipe pressure around it to hold it on seat, and a cam on the back of the controller pushes it off seat when the controller is in the center position. The "defeat" latch simply wedges another ball check valve against its seat, cutting off the exhaust of pilot valve air. However, some air will invariably leak around the cam follower pin, and the idea of trying to hold the ball ON its seat against pressure below is exactly backwards. As a result, all of these things leak a little when the handle is let go and the latch is in. Evidently the leakage is not enough to trip the deadman's application relay valve. |
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