Some of you may laugh at the old Tyco two bay operating hoppers cars as being a kids toy, but they do have a well designed clam-shell dump gate. Mechanical heart valves have a similar clam-shell design and are about the same size? Those have to work all the time and so do these cheep old Tyco cars.
I dissambeled each car and added the stirrup steps, trucks, couplers and Brake Wheel (Details West # 6401), then painted the cars using Scalecoat, Tuscan Red. Let the paint dry for a few days before re assemblying, decals and weathering with latex washes. You will notice that I emery papered each side the clam-shell dump gates on a hard flat surface after painting. This sharp edge makes for a snug closed fit, this so loose gravel doesn't slip through while running along the right of way. This method works well.
This is the Dump Pit. The plastic ties were cut and removed with the rail still left in place. A 1/4 inch dia. hole was drilled through in the center of the track and a small square rasp file was used to make a "V" shaped pit. A little spackle was spread on the pit sides and sanded, then painted with a concrete color.
Shown here is a Cross Section of what the Dump Pit looks like. The Hopper Gate Spreader Bar can be pushed down out of the way when the pit is not in use. I cut off the Kadee uncoupling pins on these cars so they do not interfear with the Hopper Gate Spreader Bar.
The grate or what is known in the mineral industry as a "grizzly" is a safety feature and prevents oversized material from getting through. Several workers with sledge hammers nearby will be added to take care of a potential problem after the cars are unloaded.
After the styrene frame is made and painted a concrete color, set in place under the rails. Drill two a 1/16 inch dia. holes into the layout as shown for the Hopper Gate Spreader Bar. There will be enough friction to hold the Hopper Gate Spreader Bar in the up position when in use.
Here is shown one of the hoppers full of gravel. Yes, real river gravel is used that was sifted and a magnet used to remove any iron. The size of gravel (sand grains) is really important in order for the Tyco hoppers to unload correctly.