The operators say that once in a while the forks will stop while lifting. They can still hear the pump motor running and the lever seems to make it speed up like it should but the forks won't raise. The height and load weight make no differance when it happens. Lowering has no problems. I looked at the control valve and there is some sort of non electric block valve bolted on it between the lift hose and the main control valve. It has a adjustment screw on it also. It seems as if this may be blocking the oil flow somehow. Any ideas. Thanks.