Here is a cut-away view of the E-47 Sump Base casting. It is to show the path of the fluid from the Gear Pump to the PA Block. You can see why it would be a problem replacing the Drain Plugs with a bolt, or a solid Pipe Plug; it would block the flow of fluid through the port and Filter. The inset shows the Fluid enters the Gear Pump from the Sump Base, passes through the Gear Pump, then through the Pump Check Valve, through the High Pressure Filter, on to the B Valve (which is not energized) and then to the C Valve (again, not energized) and then out to the Passenger Side PA Ram. This makes the plow go left. This is why Left is called the “default”. There is no Valve energized to make the plow angle left.
Here you can see the three ports on the side of the Sump Base, and what their functions are.
Moving back to the front, the lower Filter is where all the fluid leaving the Lift Cylinder passes through on its way to the A Valve when the plow is lowered.
Using the yellow zip tie to show the passageway from under the Lift Cylinder to the lower Filter port.
Here is a top view of the Meyer E-47 Sump Base showing what each port is used for.
Top view showing the passageway from the lower Filter port to the A Valve using a piece of wire.
Using the yellow zip tie to show the passageway from the B Valve to the bottom of the Lift Cylinder cavity.
Top view to show the passageway from the PA Block to the Lift Cylinder cavity
Hopefully this will give you a better understanding of how the Sump Base works. This same Sump Base is used on the Meyer E-46, E-47, E-57, and even the E-58H. The difference between this Sump Base and the E-58H Sump Base is that the E-58H Sump Base does not have the A Valve port in the back. Because the A Valve is in the PA Block, it uses the B Valve port (that is used to supply fluid to the Lift Cylinder and raise the plow) to divert fluid back to the Sump Base. There is a Cavity Plug you can use to replace the A Valve, then the E-46, E-47, E-57 Sump Base can be used on an E-58H. So if you run the E-57 and E-58H and you want to have a spare Sump Base on hand, buy the E-47 / E-57 Sump Base, and the Cavity Plug, and then the spare Sump Base will work with either pump. If you bought the E-58H Sump Base, it would only be good for the E-58H.