Installing radios in vacuum cleaners Mounting communication systems in vac trucks and fuel trucks poses some unique problems. Make careful plans, check with the operator and check with other experts such as fire officials to ensure a successful installati
Radio technicians have the opportunity to install radio equipment in unusual vehicles from time to time. This month, the subject is vacuum (vac) trucks and fuel trucks. These trucks offer a similar yet slightly different set of problems to the installer. Both types of vehicles have large hydraulic systems and either a separate power source or an engine-driven (PTO) pump system.
HAZMAT vac truck The vac truck shown in Photo 1 to the left is used for a variety of functions. A large metal container, either cubic or cylindrical, is mounted on the rear of the truck and is actually a kind of giant vacuum cleaner “bag.” Under this container are one or more water tanks feeding into an engine-driven pump and then on to a reeled outlet hose on the front of the vehicle. An engine-driven fan draws air from the container, reducing its air pressure to a level well below ambient (outside) air pressure. The inlet to this container usually has a reinforced hose set, which is used to vacuum up water, gravel, debris or other liquids and solids as desired. Certain nonexplosive petroleum products, such as oil from oil-water separators in urban drain systems, can be removed by this vac truck.
*Radio installation problems — The basis of the vac system is a large, commercial, heavy-duty truck. Once the large container and water tank(s) are fitted to the truck, an extensive hydraulic control system is put in. The large, hinged, collection container can be raised at one end to dump recovered material. The tanks, hydraulic controls and movable container pose distinct challenges to the radio installer. Antenna, receive-and-transmit (R/T) unit mounts and power cable routing require planning. Mounting antennas on the collection container, in almost all cases, is ruled out. Fortunately, most vac trucks have exterior battery boxes, so access to power is generally easy.
The first step, after some basic planning, is to mount the R/T unit and control head firmly in place. Use care to avoid hydraulic control lines and levers in the cab. Check, or have the operator check, all of the controls to be sure that they operate normally before you proceed. The back of the operator’s cab and the floor to the rear of the cab are full of control lines, so using a dash mount or an aftermarket pedestal floor mount may be a good choice. Mounting the speaker so it will be near the operator’s head when the operator is seated in the cab will help the operator to hear the radio over the noise inherent in these vehicles. Good positions are on the cab’s ceiling or above the door. An audio amplifier and an external speaker may be part of the install package. Take care that the speaker will not be exposed to too much engine compartment heat if you mount the speaker driver on the fender.
Once the R/T units are in place, power cabling is next. The battery systems are generally simple, with separate batteries for the main (road drive) and the hydraulic and vacuum drive motor. Once the cables are in place and protected from damage, insert a low-voltage cutout or magnetic switch to protect the battery from being drained and to protect the radio from transient voltages generated by the engine starter motor. Use grommets or other chafe buffers to protect wiring where it passes through the wall of the operator cab or near moving elements of the hydraulic system. Always take a moment to check the voltage of the battery you choose to use as a power source for the radio, because the hydraulic and vacuum drive system engine’s charging subsystem may not have as much voltage regulation as the truck battery. In any case, fuse both the positive and negative lines as close to the battery as possible. Mark the vehicle maintenance records to show battery connections, cable routes and the locations and values of fuses.
Antennas mounted on the roofs of these vehicles face short, tough lives. The collection hose assembly is routed over the top of the operator’s cab, so any antenna mounted there would be struck repeatedly by a large, heavy hose and metal support structures. A short “gallows boom” is built across the cab roof, but is short in relation to the size of the average antenna. (See Photo 2 on page 28.) If there is no suitable place for a whip antenna on the roof, a directional discontinuity ring radiator antenna made by Com-Rad Industries, Wilson, NY, could be a good choice. A glass-mount antenna or even a ball-mount on the side of the cab are worth considering for a protected antenna system. The hood of the vehicle may be the last antenna mounting position that you would want to consider unless you can be certain to protect the feedline from heat generated by the engine.
HAZMAT truck For hazardous materials (HAZMAT) spills, a similar vac truck system may be used to recover liquid or semi-solid materials. Generally, any radio equipment installed in such vehicles should be rated as intrinsically safe. Many of the hazardous materials are flammable or explosive at certain concentrations (LEL or density), so all spark sources must be eliminated.
*Radio installation problems — To further complicate communication, workers may be wearing respirators and gloves. Have the operators check out the communications before you turn over the finished installation. Using oversized mic switches or placing speakers in unlikely positions may be required to overcome the limitations on the operator’s ability to manipulate small objects and to hear well when wearing the personal protective equipment (PPE). In some cases self-contained breathing apparatus (SCBA) may be used.
There are a host of accessories developed for use with fire protective equipment. Both HAZMAT and fire equipment operators use similar PPE. If the HAZMAT operating environment is new to you or your company, call some suppliers or the fire department to see what solutions they have found to be successful. As an aside, if the equipment (vac truck or other radio-equipped vehicle) is routinely used for HAZMAT recovery or transportation, increase the frequency of your inspections for corrosion, because fumes or vapors from these types of materials can be extremely corrosive.
Fuel trucks Fuel trucks present similar problems to those of HAZMAT and fire trucks, but they may require different solutions. Briefly, a fuel truck is a large tank and pump system mounted on a purpose-built chassis. These behemoths rarely leave the immediate area of the airport flightline and are equipped with marker strobes and extensive grounding systems. Installing radios with these features in place requires some planning. Intrinsically safe radio systems may or may not be required, based on the type and volatility of the fuel carried. Check with the operator, customer or fire officials. Asking the local fire code experts beats trying to read and interpret complex regulations.
*Radio installation problems — Positioning the R/T unit is usually easy. Because of the sheer size of the vehicle, the cabs are uncluttered and offer lots of potential mounting possibilities. (See Photo 3 on page 28.) Where care must be exercised is in the routing and connection of power wiring to the installed radio. Always check with the operator or maintenance supervisor before routing the power leads. Make sure that power scheme meets with their approval for safety’s sake. Because these trucks have extensive grounding systems, “sneak” circuits are a real concern.
Sneak circuits are (with apologies to computer enthusiasts) “virtual” circuits that are formed when installed equipment allows current to flow around fuses or control switches. This phenomenon may seem puzzling, but is one of the key reasons I insist on putting fuses in both the positive and negative power lines for communications equipment. If you have not experienced this problem yet, that’s fine, but do not overlook the simple safety step of fusing the power leads to prevent damage to equipment or vehicles.
Mounting antennas on fuel trucks is straightforward. In Photo 4 on page 28, you can see a glass-mount antenna that resolves two important points. This type of antenna mount reduces the concern about sneak circuits. It has the added bonus of reducing–if not eliminating–corrosion of the antenna mount where it touches the truck body. As always, follow the manufacturer’s instructions and thoroughly clean the windows before installation. This cleaning is even more important in cold-weather operation areas. High-gain antennas mounted on the roof of the operator’s cab may be inappropriate because of clearance problems with aircraft wing or fuselage surfaces. Check to be sure.
Mounting communication systems in vac trucks and fuel trucks poses some unique problems that an installer can overcome by making careful plans, by checking with the operator and by checking with other experts such as fire officials. Common installation techniques may cause sneak circuits to form that must be countered. Care and common sense should be enough to provide a professional, trouble-free installation. Thanks to Anthony Aquilano, Ernie Stoitenberg and Dan Schorr for the help and information on these “invisible” service vehicles.