The designer should keep the following in mind when laying out the pumping system:
1. Suction and discharge piping should be as short and straight as possible to avoid ex- cessive friction losses. Reducers in the piping should be eccentric.
2. Pumps should not support piping.
3. Line sizes should not be smaller than the pump nozzles.
4. The suction line should be of greater diam- eter than the suction nozzle of the pump. 5. High points in suction piping, which can pro-
mote the formation of air pockets, should be avoided.
6. Pumps should be located below the suction- side liquid level, where possible.
7. A nonslam check valve should be installed in the discharge piping to protect against sudden surges and reverse rotation of the impeller.
8. Where a discharge line of greater diameter than the discharge nozzle is employed, an eccentric increaser, check valve, and gate valve (in that order) should be used.
9. A line strainer in the pump suction piping should be provided, unless the pump is equipped with a nonclog impeller.
10. Pumps should be checked for correct align- ment at the time of installation.
11. Pump suction lines should be checked for tightness to avoid drawing air into the pump. Entrained air tends to accumulate in the cen- ter of the impeller and causes a reduction in developed head and air lock.
12. When pump suction is directly connected to an open, shallow tank, baffles should be placed at the entrance of the suction pipe to break up any vortexes and to cause the inci- dence of the entrained air entering the pump to air lock.
13. When cavitation is diagnosed as the source of pump noise (characteristically, a crack- ling sound), installation of a throttling valve in the discharge piping used to reduce pump capacity should materially reduce the prob- lem.
14. Noise may arise from any of the following conditions:
A. Excessive velocities in the interconnect- ing piping or from improperly supported piping.
B. Motor and/or bearing noise in high-speed pumps.
C. Poor selection, with operating point sub- stantially higher or lower than manufacturer’s recommended “best effi- ciency point.”
D. Excessive vibration of pump or driver caused by misalignment, bent shaft, loose mounts or unbalanced hydraulic forces acting on impeller.
E. Improper installation and sizing of the piping, which may cause noise transmis- sion to the building.
F. Improper vibration mounting of pumps. 15. Reverse rotation of impeller or impeller in- stalled in reverse direction (though direction of rotation is correct), results in substantially reduced developed head and capacity with a higher power demand than the manufacturer indicates for measured flow rate.
16. Lack of liquid delivery can be due to lack of prime, insufficient available NPSH, clogged strainer, or system total head at zero capac- ity.
17. Loss of pump prime while operating can be due to loss of suction-line liquid vaporizing in suction line.
18. Excessive pump power can be due to exces- sive impeller speed, tight shaft packing, lack of sufficient clearance between impeller and casing, or higher than specified liquid den- sity or viscosity, in addition to other contributing causes mentioned above.
Piping
Insulation
5
Insulation and its ancillary components are a major consideration in the design and installa- tion of the plumbing and piping systems of modern buildings. The insulation and methods discussed are used on a regular basis primarily for plumbing and drainage work. Insulation is used for the following purposes:
1. The retardation of heat or cooling tempera- ture loss through pipe.
2. The elimination of condensation on piping 3. Personnel protection by keeping the surface
temperature low enough to touch.
4. The appearance of the pipe, where aesthetics are important.
5. The protection of pipe from abrasion or dam- age from external forces.
6. The reduction of noise from a piping system. To make certain that the reader understands the mechanism of heat, the following glossary of terms has been provided.
GLOSSARY
British thermal unit (Btu) The heat required to raise the temperature of 1 lb of water 1° Fahr- enheit.
Conductance Also known as “conductivity,” this measures the flow of heat through an arbitrary thickness of material, rather than the 1-in. thick- ness used in thermal conductivity. (See also “thermal conductivity.”)
Convection The large-scale movement of heat through a fluid (liquid or gas). It cannot occur through a solid. The difference in density be- tween hot and cold fluids will produce a natural movement of heat.
Degree Celsius This is the measurement used in international standard (SI) units and is found by dividing the ice point and steam point of wa- ter into 100 divisions.
Degree Fahrenheit This is the measurement used in inch-pound (IP) units and is found by dividing the ice point and steam point of water into 180 divisions.
Heat A type of energy that is produced by the movement of molecules. The more movement of molecules, the more heat. All heat (and move- ment) stops at absolute zero. It flows from a warmer body to a cooler body. It is calculated in such units such as Btu, calories, or watt-hours. Kilocalorie (kcal) The heat required to raise 1 kilogram of water 1° Celsius.
Thermal conductivity The ability of a specific solid to conduct heat. This is measured in Btu/ h and is referred to as the “k” factor. The stan- dard used in the measurement is the heat that will flow in 1 hour through a material 1 in. thick, with a temperature difference of 1° Fahrenheit over an area of 1 ft.2 The metric equivalent is
watts per square meter per degree kelvin (W/ m2/K). As the “k” factor increases, so does the
flow of heat.
Thermal resistance Abbreviated “R,” this is the reciprocal of the conductance value. (See “conductance.”)
Thermal transmittance Known as the “U” fac- tor, this is the rate of flow, measured in thermal resistance, through several different layers of materials taken together as a whole. It is mea- sured in Btu per hour per square foot per degree Fahrenheit (Btu/h/ft2/°F).