GMPheli
Key Veteran
Location: W. Bridgewater, MA USA
My Posts This: Topic Forum | #8 on the left daigram says Perry pump with regulator spring stretched to twice its original length. This is the spring that sets the pressure of the regulator. A regulator is a diaphram with a spring pushing on one side. On the other side is a valve that lets fuel from the pump in when the diaphram is pushed by the spring. There is also the outlet from the regulator here. The fuel from the pump comes through the valve, into the diaphram area, and out the exit. Lets say you have the fuel line disconnected and are checking to see if it pumps. There is no pressure building up because you have an open line. The spring holds the valve on the diaphram open so the fuel can go through unrestricted and just spews out the line. Now squeeze that line and start restricting the flow. The pressure will start to build up. When this pressure that is now on the diaphram exceeds that of the spring the regulation starts to happen. The diaphram moves as the spring compresses, this in turn shuts off the valve, stopping the fuel flow until the pressure drops below the spring. Thus a regulated pump, it will never exceed a certain pressure. Curtis says to stretch this spring to twice it original length, thus increasing the pressure of the pump. But his plumbing uses a return line through a check valve to the tank. This return line will prevent pressure from ever building up so I don't see the point of stretching the spring. I know in Curtis's setup the return line will have to fight the muffler pressure, but I would think the pump would put out significantly more pressure than a muffler, if it didn't then why use it? Nor do I see the point of using muffler pressure in the first place as you have the pump to do the work. The check valve and the return line lets you use a conventional carb as it is a low pressure pumped system. If you did not use the return line you would need a pump carb that is designed for higher pressure. Hope this helps and makes sense to you. I plan on trying a pump on my next ship. I am going to use the check valve and return line, but without muffler pressure (this will also let me use a fuel magnet without worries), and I am not going to stretch the spring of the pump. |
