Parallel Pump
Pumping Systems: Parallel and Series Configurations For some piping system designs, it may be desirable to consider a multiple pump system to meet the design requirements. Two typical options include parallel and series configurations of pumps. Specific performance criteria must be met when considering these options. Given a piping system which has a known design flow rate and head requirements, Qdes, hdes, the following pump selection criteria apply. Pumps in Parallel: Assuming that the pumps are identical, each pump must provide the following: Q(pump) = 0.5 Qdes h(pump) = hdes
Pumps in Series: Assuming that the pumps are identical, each pump must provide the following: Q (pump) = Qdes h(pump) = 0.5 hdes For example, if the design point for a given piping system were Qdes = 600 gpm, and hsys = 270 ft, the following pump selection criteria would apply: 1. Single pump system 2. Parallel pump system Q(pump) = 600 gpm, hp = 270 ft Q(pump) = 300 gpm, hp = 270 ft for each of the two pumps 3. Series pump system Q(pump) = 600 gpm, hp = 135 ft for each of the two pumps
Example 11.6 It is desired to use the 32 in. pump of Fig. 11.7a at 1170 rpm to pump water at 60˚C from one reservoir to another 120 ft higher through 1500 ft of 16 in. ID pipe with f = 0.030. Determine the operating point (hp & Q) and the pump power requirements and efficiency. Fig. E11.6 Head and system curves vs Q Neglecting minor losses, the energy equation can be written between the surfaces of the two reservoirs. Note that for these conditions the velocities at the reservoir surfaces is zero and kinetic energy change can be neglected.
V2 f L 0.030 ⋅1500 ft V 2 H s = z2 − z1 + = 120 ft + 2g D 1.333 ft 2 g
Since from continuity we know that Q = V A = (π D /4) V, the energy equation becomes
2
H s = 120 ft + 0.269 Q H s = 120 ft + 1.335 Q
2
with Q in ft /s
3
Converting the flow rate Q to thousands of gal/min to be consistent with Fig. 11.7a we obtain
2
with Q in 10 gpm
3
Pumps in Series: Assuming that the pumps are identical, each pump must provide the following: Q (pump) = Qdes h(pump) = 0.5 hdes For example, if the design point for a given piping system were Qdes = 600 gpm, and hsys = 270 ft, the following pump selection criteria would apply: 1. Single pump system 2. Parallel pump system Q(pump) = 600 gpm, hp = 270 ft Q(pump) = 300 gpm, hp = 270 ft for each of the two pumps 3. Series pump system Q(pump) = 600 gpm, hp = 135 ft for each of the two pumps
Example 11.6 It is desired to use the 32 in. pump of Fig. 11.7a at 1170 rpm to pump water at 60˚C from one reservoir to another 120 ft higher through 1500 ft of 16 in. ID pipe with f = 0.030. Determine the operating point (hp & Q) and the pump power requirements and efficiency. Fig. E11.6 Head and system curves vs Q Neglecting minor losses, the energy equation can be written between the surfaces of the two reservoirs. Note that for these conditions the velocities at the reservoir surfaces is zero and kinetic energy change can be neglected.
V2 f L 0.030 ⋅1500 ft V 2 H s = z2 − z1 + = 120 ft + 2g D 1.333 ft 2 g
Since from continuity we know that Q = V A = (π D /4) V, the energy equation becomes
2
H s = 120 ft + 0.269 Q H s = 120 ft + 1.335 Q
2
with Q in ft /s
3
Converting the flow rate Q to thousands of gal/min to be consistent with Fig. 11.7a we obtain
2
with Q in 10 gpm
3