PUMPS SELECTION
1. Introduction
Pumps are the fluid moving machineries which increase the mechanical energy of the fluids to be displaced. The energy increase may be used to increase the velocity, the pressure or the elevation of the fluids. A large number of pumps, differing widely in principle and mechanical construction, have been developed to meet a wide variety of operating conditions. For selection of pumps for a specific application requires the knowledge of operating conditions of the system and applicability of different available pumps. By far the most common method of adding energy is by Positive displacement or Centrifugal action, which can be supplied by the outside forces. These methods lead to the two major classes of fluid moving machinery: 1. Applying direct pressure to the fluids e.g. Positive Displacement Pumps 2. Using torque to generate rotation e.g. Centrifugal Pumps.
CENTRIFUGAL PUMPS :
The mechanical energy of the liquid is increased by centrifugal action. Centrifugal pumps are classified as single suction and double suction pumps depending upon the suction from either one side or from both sides respectively.
METHODS OF SELECITON
Pumps are usually selected by any of the following three methods: (1) the prospective purchaser supplies one or more manufacturers with complete details of the pumping conditions and requests a recommendation and bid on the units which appear best suited for the conditions, (2) the purchaser makes a complete calculation of the pumping system and then chooses a suitable unit from current catalogs and rating charts, or (3) a combination of these two methods is used to arrive at the final selection. The essential data required by any pump manufacturer before a recommendation and bid can be prepared are:
1: . Number of units required
2. Nature of the liquid to be pumped
Is the liquid?
a. Fresh or salt water, acid or alkali, oil, gasoline, slurry, or paper stock?
b. Cold or hot and if hot, at what temperature? What is the vapor pressure of the liquid at the pumping temperature?
c. What is its specific gravity?
d. Is it viscous or non-viscous?
e. Clear and free from suspended foreign matter or dirty and gritty? If the latter, what is the size and nature of the solids, and are they abrasive? If the liquid is of a pulpy nature, what is the consistency expressed either in percentage or in 1b per cubic ft of liquid? What is the suspended material?
f. What is the chemical analysis, pH value, etc.? What are the expected variations of this analysis? If corrosive, what has been the past experience, both with successful materials and with unsatisfactory materials?
3. Capacity :What are the required capacity as well as the minimum and maximum amount of liquid, the pump will ever be called upon to deliver?
4. Suction Conditions Is there:
a. A suction lift?
b. Or a suction head?
c. What are the length and diameter of the suction pipe?
5. Discharge conditions
a. What is the static head? Is it constant or variable?
b. What is the friction head?
c. What is the maximum discharge pressure against which the pump must deliver the liquid?
6. Total Head : Variations in items 4 and 5 will cause variations in the total head.
7. Is the service continuous or intermittent?
8. Is the pump to be installed in a horizontal or vertical position?
a. In a wet pit?
b. In a dry pit?
9. What type of power is available to drive the pump and what are the characteristics of this power?
10. What space, weight, or transportation limitations are involved?
11. Location of installation
a. Geographical location
b. Elevation above sea level
c. Indoor or outdoor installation
d. Range of ambient temperatures
12. Are there any special requirements or marked preferences with respect to the design, construction, or performance of the pump?
In quick estimates, for convenience, below written 5 steps are related to size class, and best buy.
1. Sketching the pump and piping layout
2. Determining the capacity
3. Finding the total head
4. Studying the liquid conditions
5. Choosing the class and type Studying the layout, capacity and head furnishes the first clue as to what class of pump is suitable. For example, where high-head small-capacity service is required, a reciprocating pump would probably suitable.
कोई टिप्पणी नहीं:
एक टिप्पणी भेजें