Pumps pressure head

Let s consider now a system with dynamic pressures and a constant elevation. A classic example of this would be where a pump feeds a sealed reactor vessel, or boiler. The fluid level in the reactor would be more or less static in relation to the pump. The resistances in the piping, the Hf and Hv, would be mostly static although they would go up with flow. The Hp, pressure head would change with temperature. Consider Figure 8-14. 

Process flow diagrams are more complex and show all main flow streams including valves to enhance the understanding of the process as well as pressures and temperatures on all feed and product lines within all major vessels and in and out of headers and heat exchangers, and points of pressure and temperature control. Also, information on construction materials, pump capacities and pressure heads, compressor horsepower, and vessel design pressures and temperatures are shown when necessary for clarity. In addition, process flow diagrams usually show major components of control loops along with key utilities. 

Volume 1 explains that pumps ean be classified as either positive-displacement or kinetie. The same is true for compressors. In a positive displacement compressor the gas is transported from low pressure to high pressure in a device that reduces its volume and thus inereases its pressure. The most common type of positive displacement eompressors are reeiprocating and rotary (serew or vane) just as was the ease for pumps. Kinetic compressors impart a veloeity head to the gas, which is then converted to a pressure head in accordance with Bernoulli s Law as the gas is slowed down to the velocity in the discharge line. Just as was the case with pumps, centrifugal compressors are the only form of kinetic compressor commonly used. 

Note when used for pump system balance, this Zhf must be used as a negative number ( — 0.1863) because it is a pressure loss associated with the fluid flowing. For pipe line sizing, the pressure head on the tank of 5 psig and any elevation difference between tank outlet nozzle and pump suction centerline do not enter into the calculations. 

Figure 3-40C. Pressure head. (Adapted by permission. Centrifugal Pumps Fundamentals, Ingersoll-Rand Co., Washington, N.J. 07882.)...

Note that both the discharge and suction pressures must be on the same base/units. These illustrations are for static head only, while overall (he pump has to work against the static and the pressure heads. (To be discussed.)... 

For general service the average centrifugal pump should lift about 15 feet of water on its suction side. However, since each process situation is different, it is not sufficient to assume that a particular pump wll perform the needed suction lift. Actually, certain styles or models of a manufacturer s pumps are often specially adapted to high lift conditions. On the other hand it is unnecessary to select a high lift pump when pressure head or flooded suction conditions prevail. Proper evaluation of suction lift conditions cannot be over emphasized. 

The capacity of this type of pump depends on the pressure head against which the pump must act (see Figure 3-49). 

Another centrifugal pump classification is whether the pump is a single-stage pump (the pressure head is developed by a single impeller) or a multistage pump (the pressure head is developed by two or more impellers). 

Decrease in pump pressure. When less dense formation fluid enters the borehole, the hydrostatic head in the annulus is decreased thus, the pressure supplied by mud pumps is decreased. Although reduction in pump pressure... 

Factory tests establish the pressure head, power, efficiency and NPSH over the complete flow range the pump can deliver running at design speed. British Standard, DIN standard or ANSI standard codes or national variations from such main codes lay down the manner of test procedure, and a minimum requirement is quite often defined by industry codes such as API 610. This is not the place to discuss instrument accuracy, as the codes lay down the limits possible from conventional instruments. There are two main classes of test the commercial requirements normally possible in the maker s test plant and high-accuracy tests that are only possible by using substandard instruments and very sophisticated techniques. 

Since the oil pump inlet is at sump (suction) pressure, a pressure gauge on the pump discharge will indicate the total pressure at that point above atmospheric, i.e. suction (gauge) plus pump head. Any detection element for true oil pump pressure must sense both suction and pump outlet pressures and transduce the difference. Oil safety cut-outs have pipe connections to both sides of the oil pump and two internal bellows are opposed to measure the difference. 

The pumping pressure required on the melts entering the different designed die heads differs to meet their melt flow patterns within the die cavities. The pressure usually varies as follows (1) blown and lay-flat films at 13.8-41.3 MPa (2000-6000 psi) (2) cast film, sheet, and pipe at 3.5-27.6 MPa (500-4000 psi) (3) wire coating at 10.3-55.1 MPa (1500-8000 psi), and (4) monofilament at 6.9-20.7 MPa (1000-3000 psi). 

Centrifugal pumps, 181 Discharge systems, 187 Example calculation, 186 Flow friction losses, 185. 186 Friction losses, pipe, see Chapter 2 Friction, 188 Pressure head, 184—186 Static head, 184-186 Suction head, 184, 185 Suction lift, 184, 185 Suction systems, 186 Hvdroclones, 265—267 Application system, 267 Ignition, flammable mixtures, 493 Impellers, centrifugal, reducing diameter, 203 Impellers,... 

In the system shown in Figure 8.28, the pump is taking liquid from a reservoir at an absolute pressure P in which the liquid level is at a height ho above the suction point of the pump. Then, if the liquid velocity in the reservoir is negligible, the absolute pressure head hj at the suction point of the pump is obtained by applying the energy or momentum... 

Normal pump suction head (NPSH) of a pump must be in excess of a certain number, depending on the kind of pumps and the conditions, if damage is to be avoided. NPSH = (pressure at the eye of the impeller - vapor pressure)/(density). Common range is 4-20 ft. 

There are two components to the pressure head that has to be supplied by the pump in a piping system ... 

The static pressure difference will be independent of the fluid flow-rate. The dynamic loss will increase as the flow-rate is increased. It will be roughly proportional to the flow-rate squared, see equation 5.3. The system curve, or operating line, is a plot of the total pressure head versus the liquid flow-rate. The operating point of a centrifugal pump can be found by plotting the system curve on the pump s characteristic curve, see Example 5.3. 

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