制冷剂按过滤器箭头所指示的方向流动时，旁通溢流阀起作用。如果流过元件时产生过大的压力降，则旁通溢流阀稍微开启，以保持足够的气流并使全封闭压缩机的马达得到适当的冷却。当吸气过滤器安装方向与箭头所指示的方向相反时，旁通溢流阀不起作用，不管压力降多高它都不会开启，这时需接一只检修阀，以便测量经过滤芯到压缩机吸气辅助阀之间的压力降。如果吸气过滤器的旁通溢流阀不起作用，就可用此检修阀作压力测量。
By-pass valve will work while the refrigerant is flowing according to the arrow on the ZRX suction line filter drier. If there is too much pressure drop, the pass-by valve will open a little to keep the enough current and will make the compressor motor get the proper cooling. The pass-by valve will not work if make the wrong installation of the suction line filter drier. It will not open even the pressure drop is very high. In this situation, it will need an access valve to check the pressure drop that pass by the core to the compressor suction valve. If the pass-by valve on the suction line filter drier is not working, we can use access valve to check the pressure.
