Heisler Water Tank
Nelson Riedel, Nelson@NelsonsLocomotive.com
8/7/2010, last updated

The water tank is made of 1/4" thick Type 1 PVC obtained in 24" X 24" sheets from McMaster-Carr.   The sheets were cut using a plywood blade in a table saw.

The tank overall dimensions are 21 1/4" long, 14 3/4" wide and 8 3/4" high.    The dimensions of the six pieces are:

  • Top & Bottom 14 3/4" X 21 1/2"

  • Sides  8 1/4" X 21 1/2"

  • Ends 8 1/4" X 14 1/4"

An additional piece the same size as the ends was cut and used as a baffle in the middle of the tank.

The finished tank inside dimensions are 21"  X 14 1/4" X 8 1/4" which has a capacity of about 10.5 gallons.

The first attempt at making the tank was to glue the sides and ends to the bottom.   The results were unsatisfactory in that there were several large leaks and the joints seemed weak.    The joints were not of the strength one achieves gluing PCV pipe fittings together.   The major cause of the failure is probably that the joints were not smooth and tight fitting.   The tank looked really good so went to Plan B and tried plastic welding.

Plastic Welding:  The plastic welding device shown on the right was picked up at Harbor Freight (#96464) and a coil of 1/8" diameter PVC welding rod was obtained from McMaster- Carr.   For simplicity I'm going to call the welding device a gun


 The gun is connected to an air compressor for air and 115 volt AC to power the heating element.   The instructions say that air should be turned on before the power is connected and left on after the power is disconnected until the heating element cools.  The gun directs hot air onto the pieces to be welded much like an acetylene torch.   There are two adjustments, the air pressure/volume and the heat control.   After some playing with the device I set the air for very low pressure --- probably only a couple pounds and  and the heat control about mid scale.  With these settings and the tip held about 3/8" from the rod the rod turns brown (singes) after 15 seconds or so.

 I ended up welding both the inside and outside of the tanks.   The weld on the inside are corner welds.   What worked for me is to lay the rod in the corner, start heating from one end and use the bent tool made from a length of 1/8" X 1/4" CFS bar stock shown in the photo to push the rod into the joint.  Holding the pieces during this operation is a challenge.  The ~ 10" length of large diameter steel bar stock held the bottom in place and served as a vertical surface to support the side.   The top of the side will tend to bend in much like welding steel.  The operating is  slower then gas welding and it is possible to heat the pieces being welded to the point where they begin to soften all the way through.   When this happens I just stopped and let everything cool down.      

This is a close-up of the joint in the photo above.  Note the slight singing at the upper end of the rod.  The scuff marks beside the rod show that the surface of the pieces being welded were soft and marked by the tool pressing the rod into the joint.

I used this technique to weld the bottom, sides and ends together and then check for leaks.    There were  a half dozen or so.    I went back and reheated the joints that were leaking and pressed the rod into the joints again.   This is were I had some trouble getting everything too hot and the whole joint turned soft.
Once the inside was welded the outside was welded.  The next three photos are of a sample I did after the tanks were all welded.   The first step for the outside welds was to cut a slight groove in the joint using the Dremel tool.   The joint was not as clean as shown in the photo; the dust was cleaned off before taking the photo.
The outside welds were made using a procedure similar to the inside welds.  About an inch or so of the rod and joint were heated and then the rod was tamped in place.   A 4 oz ball peen hammer was used to do the tamping.   Photo shows the finished joint. Care was taken to move the gun from side to side to make sure the pieces being welded were heated along with the rod.  The pieces being welded were soft on the surface when the rod was tamped into the groove.
The sample was cut about an inch from the end to show the joint.    It's as I had hoped it would look. 

After the outside of the tank was welded  it was tested for leaks again.  There were several, mostly in the corners where three pieces came together.   Tamping the outside welds must have broken the inside welds. Reheating and tamping the outside fixed most the leaks.   In one corner the Dremel was used to cut out a length of the outside weld and it was welded again.   That worked. 

One of the attractive aspect of using plastic for the tanks is that standard plastic plumbing fittings can be attached to the tank for the ports and vents.  

Input Port: The input port was made using a standard 2" PVC pipe with domed cap.   The cap was bored slightly to make it an easy sliding fit.   The 2" pipe OD is about 2 3/8".   A 2 1/2" hole saw was used to cut the hole through the steel outer tank and the plastic tank top at the same time.  (The PVC tank top had been attached with a half dozen screws sheet metal screws.)    The oversize hole make the pipe a easy fit up through the metal outer tank. 

The end of a 2" PVC coupling was glued to the end of a short length of pipe that was to be the input port.   About 1/4" length of the upper side of the coupling was then turned in the lathe to the exact diameter of the hole cut with the hole saw.  The lower end of the coupling was cut off leaving  about 1/4" of the larger diameter to serve as a shoulder.   The upper end of the pipe was cut to the length such that the end will be about 1 5/8" above the steel tank top.   The port was then glued to the tank top.  It was later plastic welded on the under side to  make sure it stayed in place. 


Output Ports: Two output ports are required; an overflow which also serves as a vent and the output port.  Both these ports shown in the photo on the right use 1 1/2" PVC pipe.   The pipe is about 1 7/8" OD.  The holes through the tank bottom were made with a 2" hole saw.  (The holes are over open areas of the tender frame.)  

The vent on the right had a piece of coupling glued to the bottom with the end turned to match with the hole. The upper end of the vent pipe was cut off about 1/16" below the underside of the tank top.   The underside of the vent pipe will be plastic welded for strength.

This is the first photo to show the baffle which was welded in the middle of the tank.
Some years ago Dan Staron mentioned that he would use a sump on his next water tank--- it sounded like a great idea.  A clean out plug threaded adapter and plug proved to be an ideal sump.  

The outside of the adapter is about 2 1/4" diameter. A piece of pipe was glued in the adapter and the end cut off leaving a little over 1/4" length of the pipe end of the adapter with the pipe inside.  The last 1/4" of the outside of the pipe end was then turned down to the exact diameter of the hole made by the 2" hole saw.   The adapter was then glued to the tank bottom.  The top of the adapter is flush with upper side of the tank bottom so all the water should make  it to the sump.

The square end of the cleanout plug is hollow so a piece of the 1/4" PVC sheet was glued inside the pug to give more thickness and a 1/4" NPT hole was then drilled and tapped through the plug. (The output fittings use 1/8" pipe but the 1/8" pipe threads looked too fine to hold in the plastic.)

The screen is a 50 mesh  McMaster part # 98755K11 Miniature PVC Suction Strainer.  The very end of the plug was bored slightly so that the strainer would slide into the open end of the plug.  It was then glued in place. 

The photos on the right show the vent and the sump.

At this point the top of the tank is held in place by six screws.  A bead of caulk was run along the seam to make it watertight.   I'll probably scrape off the caulk and plastic weld the seam in the near future.  

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