BOILER CHECK VALVE
   

boiler check valve located at the right rear top of the boiler

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.

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 door where people can pass through in one direction but not return through the door from where they came.  Once a fluid passes through a check valve it can not return back through the check valve to its source (see the discussion on the water check valve for a description of how a check valve operates).

Water from the water supply tank is pumped by the power water pumps through the feed water heater to preheat it before entering the boiler when the water automatic senses low water in the boiler and calls for water to be pumped into the boiler.  The boiler check valve inhibits steam and hot water from the boiler from being forced back out of the boiler through the water feed line when water flow to the boiler is stopped.

 

BOILER CHECK VALVE AND THE BOILER STAND PIPE

As Stanley originally intended the check valve at the boiler to be used in an emergency it is designed a little different than a standard check valve.  The bottom of the check valve is designed to function like a Stanley's hand valve.  The bottom of the check valve includes a threaded L-shaped valve stem and a valve nut and valve stem packing as found on any hand valve on a Stanley.  When the L-shaped valve stem is turned such that it threads into the base of the check valve (the L-shaped valve stem shown in the diagram is rotated counter-clockwise) it makes contact with the check ball and raises it off its seat.  Thus water can pass through the check valve into the boiler but it can also pass back out of the boiler and into the piping supplying water to the boiler.

With the check ball held off of its seat by the L-shaped valve stem, the check valve would not function only permitting water to flow into the boiler.  If the piping diagram is reviewed it becomes obvious that the piping of the feed water heater would always be a boiler pressure since it is effectively part of the boiler.  While the pumps are supplying water to the boiler the feed water heater piping is subjected to pressures higher than that of the boiler simply because the pressure of the water must be higher than that of the steam pressure of the boiler if water is to be pushed past the (emergency) boiler check valve and into the boiler.  However, there is no need to maintain the feed water heater piping at boiler pressure and thus by allowing the (emergency) boiler check valve to function as a check valve boiler pressure can be relieved on the feed water heater piping to only when the pumps are supplying water to the boiler.

A problem was also discovered with the (emergency) boiler check valve if the check ball were held off of its seat by the L-shaped valve stem.  The ball, in not bouncing on and off the seat would become covered with steam cylinder oil over time as the steam cylinder oil circulated in the water supply system.  This coating would allow minerals and other deposits in the water not captured by the strainer in the water supply tank to collect on the oil film.  The same action would occur on the check valve seat.  When the (emergency) check valve was required and the L-shaped valve stem was turned (clockwise) to allow the check ball to be seated, the buildup of oil and deposits on the check ball and valve seat would not allow a good seal and the check valve would not block the flow of steam and water back out of the boiler and into the water supply piping.  By allowing the (emergency) boiler check valve to function continuously it keeps the check ball and check valve seat free of oil and deposit accumulation and thus functions properly.

The (emergency) boiler check valve is connected to and supported by a pipe that feeds to the top of the boiler.  Examination of the photo at the right shows the (emergency) boiler check valve connected to the boiler feed pipe.  The top of the boiler is drilled for 1/4" NPT pipe.  A 1/4" NPT Tee is used to make the connection to the top of the boiler as shown in the photograph.  The end of the Tee that is screwed into the boiler has a special close nipple attached to it.  One end of the nipple has a 16" length of copper or stainless steel tubing welded in place such that the inside diameter of the nipple and the outside diameter of the tubing are nearly the same.  The tubing is inserted partway into the nipple and then welded in place.  This assembly forms an inverted stand pipe within the boiler.

The purpose of the stand pipe is to insure the cooler water being fed into the boiler is fed directly into the hot water already in the boiler.  Thus the cooler water added to the boiler is being mixed with the hot water already in the boiler.  This prevents a thermal shock from occurring.  Had the water being fed to the boiler been simply plumbed to the top of the boiler and allowed to cascade into the boiler, it would come in contact with the hot flues and subject them to thermal stresses which would, over time, cause premature metal fatigue and failure.  By the inverted stand pipe being 16" long it assures that water entering the boiler is released below the water line where it can mix with the water already in the boiler (Model 735 boilers were 18" tall thus the 16" stand pipe would place the water at 2" above the bottom flue sheet and hopefully 4" or more below the water level in the boiler).

In addition to the connection between the plumbing tee and the (emergency) check valve there is also a length of pipe on the remaining port of the plumbing tee.  Sitting on top of the boiler is the smokebox (not shown in the photograph) which collects up the combustion gasses and directs them to the exhaust duct (see the discussion on the smokebox).  The length of pipe connected to the top of the plumbing tee is made long enough that it will project up through the top of the smokebox.  This pipe is ended with a pipe cap.

Over time as water is pumped into the boiler the inverted stand pipe can become choked with buildup and restrict the flow of fresh water into the boiler.  The steam cylinder oil in conjunction with the dissolved minerals in the water supply will accumulate on the inside of the inverted stand pipe and reduce its inside diameter.  If not routinely maintained the accumulations will block the inverted stand pipe and no water will flow to the boiler.  The accumulations effectively become an orifice in the pipe restricting water flow.

The chocking off of the inverted stand pipe occurs slowly over time.  As a result the power water pumps are now pumping water through effectively a smaller and smaller pipe.  This causes the water pressures the power water pumps generate to become higher and higher eventually reaching the rupture point of the copper tubing.  As the buildup occurs slowly over time the driver doesn't usually notice the pumps starting to "pound" more (this situation is aggravated as the pumps are in a pump box well below the floorboards and frame well isolated from the driver by the cushioned car seats and distance).  Since the water flow to the boiler is automatically performed by the water automatic the driver is also unaware that the pumps have to function for longer periods of time to compensate for the restriction occurring (and growing over time) in the inverted stand pipe (with earlier non-condensing Stanleys the driver had to maintain the proper boiler water level by operating a valve thus there was some feedback to the astute driver that the pumps were running more than normal).

The solution is to routinely remove the cap sticking up through the smokebox on the inverted stand pipe and to run a wire down the pipe to insure any deposits and buildup on the interior of the inverted stand pipe are removed.  The deposits can become quite hard and well attached to the inverted stand pipe's interior walls and thus for extreme buildups a long drill bit may be needed to remove the deposit.  Generally, periodic (once a year nominally) cleanings with a stiff wire steel brush is all that is needed.  The distance from the pipe cap to the bottom of the boiler needs to be measured and when cleaning is performed it is important to insure the full length of the pipe is cleaned; nothing more nor nothing less.  The deposits can make one think they are hitting the bottom of the boiler when inserting the cleaning wires, drills, and brushes.  One also needs to be certain if they are using a very long drill bit that they actually haven't reached the bottom of the boiler's flue sheet by mistake and thus end up drilling through the flue sheet accidentally.

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