Stanadyne DB2 Injection Pump - How It Works

The diesel industry uses two basic styles of mechanical injection pumps: the inline and rotary. In most applications, the inline pumps are attached to inline engines (due to packaging), while the distributor style can be found on either V-shaped or inline powerplants.

In the '90s, Ford and General Motors required injection pumps for their indirect-injected V-8 diesel engine programs. The injection pumps had to be reliable, easy to service, and most importantly, easily attachable to the engines. When all the available pumps were reviewed, the Stanadyne DB2 (formerly marketed as a Roosa-Master) was both corporations' choice.

To learn more about the DB2 injection pump that was used on the Ford 6.9L and 7.3L, General Motors 5.7L, 6.2L, and 6.5L engines, Diesel Power worked with the University of Northwestern Ohio (UNOH) and staff member Bill Sergent. We also visited with injection pump specialist Brad Anderson, owner of North West Fuel Injection Service in Columbus Grove, Ohio. Anderson is very experienced in repairing, servicing, and hot-rodding the DB2.

A diesel engine is different from a conventional gasoline engine in that its cylinders are filled only with air during the intake stroke. Air in a diesel engine is compressed until it reaches extremely high temperatures and pressures, at which point fuel is sprayed into the chamber. Spontaneous combustion occurs as a result of the hot compressed air and the fuel's flash point-the combustion is used to power the downward stroke of the piston.

The fuel injection pump is important because it not only pressurizes the fuel to the mechanical injectors, but provides the required timing advance under all operating conditions.

The Origin Of The Stanadyne DB2 Pump
With the DB2, engine rpm is controlled by a rotary fuel-metering valve. When the accelerator is depressed, the throttle linkage opens the metering valve in the injection pump, allowing more fuel to be delivered to the pumping chamber. Thus, the job of the injection pump is to not only accurately time the fuel delivery to the combustion chamber, but to also control the engine speed by varying the air/fuel ratio supplied to the cylinders.

The first practical design for a rotary distributor pump was engineered by Vernon Roosa, a diesel mechanic employed by the City of New York, where he maintained and repaired diesel-driven generators. Roosa patented his design in 1941, but it took him some time to generate any interest in his invention. Following the end of World War II, the Hartford Machine and Screw Company, a machine shop best known for producing aircraft engine components for Pratt and Whitney, decided to test out the Roosa design and brought its inventor to Hartford, Connecticut, to assist in research and development.

Although the Roosa design for a rotary injection pump was not the first, it was easily the most successful and generated many copycat designs. One of these, the American Bosch (Ambac) VE, lasted into the 1990s and was employed on light-duty diesel engines, including the 5.9L Cummins. The main difference between the DB2 and the Bosch VE pump is that the VE pump is a hydromechancial sleeve-metering distributor pump that employs a single-plunger pumping element.

The attraction of the Roosa design was affordability, simplicity, and easy serviceability. The Hartford Machine and Screw Company eventually became part of the Stanadyne Corporation. Thus, the Roosa injection pump became known by the name of its new owners.