The most recognizable truck pump is the “Dump Pump”. The dump pump, as we know it today, was introduced almost 50 years ago and is little changed since, although the newest design offers larger ports and a more efficient gear design. This pump, common on dump trucks from tandem axle to dump trailers, is essentially a gear pump of slightly more than 6 cu. in. displacement with an integral three positions, three way directional control valve, and pressure relief assembly. The most important thing to keep in mind about these pumps is that they were designed specifically for one application—dump trucks (hence the name!)—and are not suitable for other common trailer applications like live floor and ejector trailers. Narrow internal paths make them unsuitable for continuous duty applications due to the likelihood of excessive heat generation. Dump pumps also have maximum pressure ratings that may fall below the requirements of some live floor applications.

Dump pumps are commonly direct-coupled to the power take-off. Weighing 70 lbs. it is vital that direct-coupled pumps be rigidly supported, via an installersupplied bracket, to the transmission case. This bracket should be a four-point (two pump/two transmission) type. Dump pumps typically provide extended body studs to use as attachment points. Refer to the PTO installation manual for additional information and design suggestions.

 Another important consideration in dump pump selection is “two-line” vs. “three line” systems. This refers to the number of hoses used to plumb the pump. Two line systems utilize a common inlet and return hose and are common on trucks that simply dump, rather than spread, materials. Three-line systems are equipped with a dedicated return hose and are preferred if the truck will be used for spreading— applying gravel to a roadbed for example. A dump pump can easily be converted from two to three-line by inserting an inexpensive sleeve into its inlet port and un-capping the return port. The sleeve blocks an internal path and neutral/return oil is directed back to tank via the return port. There is one special concern; the third (return) line must be positioned below the tank’s oil level to prevent loss of prime and subsequent pump aeration damage.

 There are at least three benefits of a three-line installation over a two-line. The primary benefit is one of efficiency. The third line allows an unobstructed return path to reservoir resulting in faster cycle times. The second benefit is system protection should an operator inadvertently leave the PTO in gear—and the pump turning—while traveling down the road. The third is that the dedicated return line allows for the installation of a return line filter to remove contaminates; an important consideration, especially if trailers are frequently switched between tractors.

 Available in both the Dynaco Hydraulic C101 Remote Mount and the C102 Direct Mount configurations, C101 and C102 dump pumps with valve are specifically designed for all kinds of dump truck. The pump body combined with control valve, built-in adjustable relief valve and one way valve, it could greatly simplify the system and installation.