Direct-Acting (Steam) Pumps

8.0 Scope

This Standard applies to direct acting (steam) pumps. It includes types and nomenclature; definitions; design and application; and installation, operation and maintenance.

8.1 Types and nomenclature

8.1.1 Introduction

A direct acting (steam) pump is a reciprocating (steam) engine and a liquid end built integrally together as a unit. Although steam is implied as the driving medium, compressed gases such as air or natural gas can be used.

8.1.2 Types

Figure 8.1 shows the relationship between the following pump types.

8.1.2.1 Horizontal pump

The axial centerline of the cylinder is horizonal.

8.1.2.2 Vertical pump

The axial centerline of the cylinder is vertical.

8.1.2.3 Double-acting pump

Liquid is discharged during both the forward and return strokes of the piston or pair of opposed plungers. That is, discharge takes place during the entire cycle (see Figures 8.2 and 8.5).

8.1.2.4 Piston pump

The liquid end contains pistons (see Figure 8.2).

8.1.2.5 Plunger pump

The liquid end contains plungers (see Figure 8.5).

8.1.2.6 Simplex pump

Contains one piston or one pair of opposed plungers driven by one steam cyclinder (see Figure 8.3).

8.1.2.7 Duplex pump

Contains two pistons or two pair of opposed plungers driven by two (steam) cyclinders (see Figure 8.4).

8.1.3 Nomenclature

8.1.3.1 Purpose

The nomenclature and definitions in these Standards were prepared to provide a means for identifying the various pump components covered by these Standards and also to serve as a common language for all who deal with this type of equipment.

The following definitions and drawings illustrate typical construction of direct acting (steam) pump components but do not necessarily represent recommended designs. Variations in design may exist without violating the intent of these standards.

8.1.3.2 Right and left hand designations

To determine the relative positions of components or hand of pump, proceed as follows:

For horizontal pumps, stand at the drive (steam) end and face the liquid end. For vertical pumps, stand facing the driver (steam) valve chest.

When standing as indicated above, the side on the left is the left hand (LH), and the side on the right is the right hand (RH) side.

8.1.3.3 Liquid end

The liquid end of a direct acting (steam) pump is the same as the liquid end of a simplex or duplex doubleacting power pump. Therefore, the table of liquid end parts, the drawings of the piston pump liquid ends and the discussion of valve seat area are also applicable to direct acting (steam) pumps.

The following liquid ends are used on both direct acting (steam) and reciprocating power pumps:

8.1.3.3.1 Piston type

The liquid end contains pistons as shown in Figure 8.2.

8.1.3.3.2 Plunger type

The liquid end contains plungers as shown in Figure 8.5. Since most direct acting (steam) pumps are double- acting, and since the conventional plunger is single- acting, two plungers and two individual pumping chambers are required for a simplex plunger pump (four of each for a duplex), arranged on a common axis as shown in Figure 8.5.

8.1.3.3.3 Valve plate type

Has removable suction and/or discharge valve deck(s) (valve plates). The drawing shows a valve plate pump with a removable discharge valve deck (see Figure 8.6).

8.1.3.3.4 Valve pot type

Has a separate cover over each valve chamber. A side valve pot type has the suction valve pots at the side of the pump (see Figure 8.7).

8.1.4 Drive (steam) end

The drive (steam) end is that portion of a direct acting (steam) pump which distinguishes it from a reciprocating power pump. It provides the force to drive the piston or plungers in the liquid end. The drive end includes the drive cylinder, drive piston(s), rods, valves, valve-actuating mechanism (valve gear), and various additional parts required to supplement the functions of the above.

Figure 8.8 shows a cross section and an exploded view of a typical horizontal duplex drive (steam) end.

8.1.4.1 Drive (steam) cylinder

This is the major component of the drive end and supports most other drive end parts. It forms the chambers which retain the gas, air or steam.

8.1.4.2 Drive (steam) piston

The drive medium (steam, gas or air) acts upon the drive piston, moving it in the desired direction. The piston rod fastened to the drive piston transmits this motion to the liquid end.

8.1.4.3 Main drive (steam) slide valve

The main drive slide valve arrangement is such that it directs high-pressure steam or gas to one end of the cylinder, simultaneously exhausting the spent steam or gas from the opposite end.

8.1.4.4 Valve gear (actuating mechanism)

The valve gear moves the main drive valve at the end of each stroke of the pump so that the drive piston reverses its direction of travel.

8.1.4.5 Auxiliary drive (steam) valve

A simplex pump is equipped with an auxiliary drive valve which is actuated by the valve gear and with steam, gas or air actuates the main drive valve. This construction is necessary to allow a simplex pump to operate at low speeds without stalling.

8.1.4.6 Types of main drive (steam) valves

The following types of steam valves are used:

8.1.4.6.1 D slide valves

D slide valves are flat valves having the general form of the letter “D” (see Figure 8.9) lying on its back. This type main drive (steam) valve is recommended for drive (steam) end operating temperatures up to 260°C (500°F).

8.1.4.6.2 Piston valves

Piston valves are circular valves fitted with self-adjusting piston rings (see Figure 8.10). This main drive (steam) valve design is recommended for drive (steam) end operating temperatures above 260°C (500°F).

8.1.4.7 Types of valve gear adjustments

The following types of valve gear adjustments are used (Figures 8.11, 8.12, and 8.13, on page 6):