water check valve originally referred to by the stanley motor carriage company as the boiler check valve

Check valves are found at several locations throughout a Stanley's water, fuel, and oil systems.  Depending on how the check valve is being used determines how the check valve is identified.  The function of a check valve is to isolate a fluid plumbing system.  The check valve can be thought of as similar in function to an airport security check point or a turnstile where people can pass through in one direction but not return through from where they came.  Once a fluid passes through a check valve it can not return back through the check valve to its source.

What is now referred to as the water check valve, Stanley originally called the boiler check valve.  The purpose of a boiler check valve is to isolate the steam and hot water pressures of the boiler from the boiler water supply system such that the pressure of the steam doesn't force water back through the pumps and into the water tank.  The check valve at the boiler that Stanley referred to as the emergency boiler check valve now serves the function of the boiler check valve (see the discussion on the boiler check valve for additional information).

What we now call the water check valve functions as a backup to the boiler check valve, and isolates water in the feed water heater from the piping of the water automatic and the water path back to the water tank.  One of the reasons for making this change is to limit the pressures on the feed water heater water tubing to pressure only when the pumps deliver water to the boiler.

The water check valve is located just in front of the firewall at the right side of the car.  A water supply pipe from the power water pumps projects through the car's frame at the lower right side of the firewall.  The water check valve's inlet port is mounted to end of the pipe.  The discharge side of the check valve is plumbed to the inlet of the feed water heater then onto the boiler via the (emergency) boiler check valve.  Another line, located in the piping before the check valve leads to the water filter, water automatic bypass valve, and the water automatic.



A Stanley check valve consists of three basic parts.  The major part is the body which includes the two ports for 1/8" NPT pipe, a machined "seat" for the check ball to sit on, and a threaded end for a cap.  The remaining two parts are the check ball, and cap.  The check ball is usually brass so that it doesn't rust however they are often replaced today with nylon balls.  The use of hard steel or stainless steel balls is to be avoided as they wear the soft bronze seat of the valve over time.  It is advantageous to have the ball made of a softer material such that it wears as it's much easier to drop in a new ball than replace the check valve because the seat has worn to the point that it no longer seals properly to the ball.  An integral part of the cap is a machined surface that determines the "lift" of the check ball or how high the ball moves off the seat.

A check valve is a simple device with one moving part ~ the check ball.  A check valve is basically a cast bronze body that is drilled to allow water to pass through it.  The valve includes a cap that can be removed to allow inspection of the check ball (dark yellow in the drawing) and the check ball seat (the part of the valve the ball sits on).

For a check valve with no water, fuel, or oil passing through it the check ball (dark yellow) is sitting on the seat.  Any volume of water (or fuel or oil for check valves in those fluid systems) that has already passed through the check valve or is "downstream" of the check valve (shown in light blue) can not pass back through the valve.  In fact any attempt for this fluid to pass back through helps to push the check ball harder into its seat thus insuring a good seal between the ball and the ball seat.  The supply fluid (dark blue) is not under any pressure since the pump (or other source of pressure) is not pumping the fluid through the valve.  The check ball firmly seated doesn't allow any of the fluid in to flow back into the supply from where it originated.
When the pumps are pumping water, fuel, or oil, the pumps are able to generate greater pressure on the supply fluid (dark blue) than the pressure of the fluid holding the check ball on its seat.  The check ball is lifted off its seat and the pumped fluid is forced past the check ball and into the piping downstream of the check valve.

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