liquid from the tank shall be by gravity and by compressed air to empty the tank of liquid
through a rear gate valve. The required partial vacuum and air pressure shall be generated by a
dual purpose pump furnished with the semitrailer and designated herein as the vacuum pump.
The vacuum pump shall be driven by an auxiliary diesel engine.
* 3.18.2 Liquid intake. A 3-inch nominal diameter, stainless steel, quick opening gate valve
for liquid intake shall be provided. Automatic means of closure conforming to DoT Safety
Regulation 178.345-6 shall be included. Liquid intake shall be through the valve at the rear top
of the tank, or at the rear bottom through a vertical standpipe, inside the tank. The standpipe
shall extend within 18 inches of the tank top and shall be provided with a baffle wear plate. The
standpipe shall be not less than 3 inches in inside diameter. The 3-inch valve shall be equipped
with a cam-lock coupler and a dust cap with security chain, all of stainless steel.
* 3.18.3 Liquid discharge. A 4-inch nominal diameter, stainless steel, quick opening gate
valve for liquid discharge shall be provided. The valve shall be at the bottom, rear of the tank.
The valve shall be equipped with a cam lock coupler and a dust cap with security chain or cable,
all of stainless steel. The valve remote control, as required by DoT Safety Regulation 178.348.
DoT-412, shall be located at the front, streetside of the semitrailer. The control shall be outlined
by a contrasting color panel at least 12 inches square, identified with the words "EMERGENCY
SHUTOFF", and provided with indicator arrows or instructions such as "PUSH", "PULL" or
other appropriate wording. Identification and instruction wording shall be in letters not less than
2 inches high.
3.18.4 Tank and vacuum pump performance. The vacuum pump shall provide sufficient
suction to cause an average water flow rate into the tank of not less than 200 gpm with a vertical
lift of 10 feet. Evacuation of liquid from the tank shall be by pressure sufficient to cause an
average water flow rate of not less than 150 gpm against a head of 15 feet, when using
compressed air from the discharge side of the vacuum pump. All inlet and outlet piping shall be
capable of passing solids up to 2-inch sphere size. Float shutoff valves shall be provided in the
liquid tank and the surge tank, capable of closing off the vacuum line, when under suction from
the vacuum pump, without transmitting any liquid to the vacuum pump when either the liquid
tank or the surge tank is filled with liquid. The tank liquid float valve and surge tank shall be
capable of preventing foam from entering the vacuum pump suction line when the semitrailer is
loading waste caustics and detergents, to within an allowable leakage tolerance of 0.02 percent of
the tank capacity collected into the tank.
* 3.18.5 Piping. All vacuum lines inside and outside the tank shall be of type 316L stainless
steel. The pipe and fittings shall be not less than 2.50 inch standard pipe size and shall be made
up in subassemblies and interconnected by boiler unions or similar quick disconnects. All liquid
suction and discharge piping shall be of type 316L stainless steel. The pipe and fittings shall be