This section highlights some common pump piping configurations. Although horizontal pumps are shown in most of the exhibits, the arrangements are typical for all types of pump applications.
Following figure illustrates the components that are usually found in pump suction and discharge piping. The suction line has a positive shut-off valve; in this example, it is a gate valve. The temporary tee-type strainer shown below catches any foreign matter that may have collected in the piping during construction.
After the suction and discharge valves have been shut off, the blind flange is unbolted and put aside and the strainer is pulled out. This strainer is generally used only for start-up. Following figure shows a basket strainer that may also be used in a pump suction line.
Although this particular strainer does not need additional fittings for its removal and cleaning if reused, it does require additional maintenance because of the downstream flanges of the valve.
The pump nozzle and possibly the base support under the elbow must he unbolted to pull the spool piece and remove the strainer.
The next common fitting is a reducer; this should be an eccentric type as shown below, with die flat side on top to reduce the possibility of cavitation in the pump.
Piping Layout Considerations
Before initiating a piping layout in a pump area, the plant layout designer must consider several factors that are critical to optimum design. The first factor concerns the support Of the pump piping, which often includes large expansion loops for flexibility.
If the pumps are located under a pipe rack or structure, support is relatively easy. If not, the plant layout de-signer must consult with the stress engineer for the best location for equipment such as stops and hangers.
Pumps in an open area often require a much larger structure for pipe supports. Allowable loading on a pump nozzle is very low, and the piping must be properly supported to avoid overstressing the nozzles.
Vendors may void pump warranties if the allowable loads are exceeded. Client pump and driver maintenance procedures must also be known at this stage, especially those regarding how each item is to be physically removed.
Very small pumps may be removed by hand; larger pumps require the use of an A-frame, as depicted below. Very large pumps may be removed by a cherry picker. The next factor to consider is duplicate piping con-figurations at groups of pumps of similar size.
For example, a new chemical plant had 203 pumps, of which almost 75% required piping ranging from 11/2 in to 3 in in diameter and had a maximum operating temperature of 230° F.
A layout designer, working with a stress/support engineer, designed the piping with a flexibility loop that was based on a 3-in line operating at 230° F.
This layout was duplicated for 76 pairs of pumps, or 152 total.
Although the piping as designed was conservative and slightly more costly for the 11/2- in and 2-in pumps, engineering, fabrication, and construction time could be reduced through standardization.
A fully dimensioned sketch of this particular standard design was given to each designer on the project. If the pumps in the designer’s area fell into the 3-in, 230° F operating temperature category, the design was copied exactly.
The 152 pumps were designed and supported once and in an identical manner. Uniformity of design in piping, supports, and steel were the results of thinking ahead.
This is what a client pays for when hiring an engineering contractor. Spending more on engineering may reduce construction costs, or spending more on materials may save both engineering and construction costs.
A pump lay-out should be viewed not on an item-by-item basis but as a whole area.
Following drawing shows an example of a standardized pump layout. The designer must also be aware of all operation and maintenance concerns with all pump layouts.
Maintenance and operational access needs are shown below.
When developing an equipment arrangement in pump areas, the layout designer must envision potential obstructions around the pumps (e.g., large block valves, steam turbine piping, and tee-type pipe sup-ports from grade).
Four feet (1,200 mm) is a generally accepted distance between pumps or associated piping. When expansion loops are required between pumps, it is necessary to partially run the lines over the pump and driver.
Every effort must be made to minimize maintenance obstructions by running the piping either outside the area directly over the pumps, or at a high enough elevation to permit the removal of the pump or driver.
Orientation of block valves must minimize the plot area required. Elevation of the valves should generally be as low as possible and common in both lines when practical.
Suction lines from below the grade
Pumps whose suction lines come from below grade are shown below. This is the one time that the reducer absolutely must have the flat side on top to avoid cavitation. Use of a basket strainer is more prac-tical in this case because the spool piece containing the strainer could be lifted out, as illustrated below.
Side Suction Pump Piping
When side suction nozzles are used on centrifugal pumps, a minimum of five diameters of straight run is added to the line before it enters the nozzle. This distributes the liquid evenly because the flow is coming in perpendicular to the impeller.
Following figure displays this configuration for a centrifugal pump.