As a petroleum supervisor, you must understand the basic workings of the types of power units used in
petroleum operations. You must also understand the operating characteristics of pumps in order to properly
supervise you subordinates.
PART A - TYPES OF POWER UNITS
There are two types of internal combustion engines: reciprocating and turbine. The reciprocating spark
ignition engine is of the gasoline burning type. The fuel is ignited by a spark plug when the piston is at the
top of the cylinder. There are two classifications of reciprocating engines: four cycle and two cycle, The
four cycle produces more power than the two cycle engine, but it is a much heavier engine than the two
cycle. Gasoline engines used in the military are generally used with small equipment such as 100 GPM
pumps (four cycle), chain saws, and outboard motors (two cycle).
The compression ignition engine functions the same as the spark ignition except it does not have spark
plugs. Heat of compression is the source of ignition. For this reason, the engine is of much heavier
construction. As the piston moves in the upward stroke, the air is compressed and heated to approximately
900 to 1000 degrees Fahrenheit. At this point fuel is forced into the chamber by means of an injector and
combustion takes place. The compression ignition engine will produce more horsepower and because of fuel
injection is much more efficient than the spark ignition engine. The cost is much more than the gasoline
engine, but there is less maintenance required. Diesel engines are very well suited for large pumps and
stationary applications where low speeds and high horsepower are required. Because diesel engines use
heat compression for ignition, they need assistance in order to start in cold weather. This is accomplished by
glow plugs or ether injection.
Turbine engines work on the principal of heat of compression, but do not use pistons to create hot air.
The air is compressed by the use of compressors and is directed to a combustion chamber where fuel is
injected and combustion takes place. The basic design is very simple and there are less moving parts than
reciprocating engines. The following are characteristics of turbine engines:
Produce more horsepower per size.
Require less maintenance.
Initial cost is very high.
Sensitive to dust and dirt.
Electric motors are used in fixed facilities because of their lower maintenance and operating cost.
Electric motors operate in a magnetic field. When energy is applied, the magnetic field is established and
creates a push-pull action which causes the armature to turn.
PART B - PRINCIPLES OF PUMPS
There are three basic types of pumps used by the Army. These are: reciprocating, rotary, and centrifugal.
Reciprocating pumps displace liquid by a reciprocating or back and forth motion. The most common
application is a piston or plunger moving back and forth in a cylinder. As the piston moves backward, a
suction is created and the liquid is drawn into the cylinder. As the piston moves forward the liquid is
expelled. When only one piston is used, it is classified as a simplex pump. When two pistons are used, it is
known as a duplex pump, this will move fluid in both directions. Because of their action, they are classified
as positive displacement pumps. These pumps create special problems.
They must be equipped with surge tanks or pressure relief valves.
They create pulsations on a pipeline.
They require a higher degree of maintenance than other types of pumping units (i.e., packing around the
piston, cooling the unit).
The pump you will see the Army use is the ROWPU, because of the high pressure required to pump the
water through the system. Advantages of the reciprocating pumps are:
High suction pressure, high discharge pressure.
Disadvantages of the reciprocating pumps are:
Must have relief valve and surge tank.