Pumps in parallel

Here we see something interesting. Recause the system is designed for both pumps running in parallel, when only one pump is operating, this pump will run to the right of its REP. This situation brings it s own peculiar set of implications, not often understood in indu.stry. 

Applied Process Design for Chemical and Petrochemical Plants 

Space Requirements Less head room Less floor area, more head room. 

Priming Flexibility (Relative to Required Usually not required 

Maintenance More accessible Major work project 

Corrosion and Abrasion No great problem Can be considerable problem 

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Use two smaller pumps in parallel. cS. U.se a larger/slower pump. 

Use two lower capacity pumps in parallel. This reduces Hf and Hi. 

Now wc can see the iniporraiiee of rlie eoneenrrie ellipses of effieieney on the pump family eurve. As mueh as possible we should find a pump whose primary effieieney are eovers the needs of the system. Certainly the needs of the system should fall within the seeond or third effieieney ares around the pump s REP. If the system s needs require the pump to eonsistently run too far to the left or right extremes on its eurve, it may be best to eonsider pumps in parallel, or series, or a eombinarion of the two, or some other arrangement, possibly a PD pump. We ll see this later. 

When this happens, you need to consider an arrangement of pumps running in parallel, or in series, or in a combination of the two. Pumps in parallel are two or more pumps working side by side, taking the... 

The solution is Identify the dominant and weak pump should they exist. To do this, take pressure gauge readings with the pumps running at shut-off head. Verify that the impellers are the same diameter, and that the wear bands and motor speeds are equal. If you can identify one pump in the pair as dominant, ahvays start the weak pump first and then add the dominant pump in parallel with the weaker. The dominant pump coming on stream w ill push open the check valve. It may be necessary to override a sequential starter. 

The reactor had a loop for each half of the core. Each circuit had two steam drums and two. 500 MW(e) turbines. Water was circulated in each of the two circuits by four pumps in parallel (8 lotal), though usually each circuit had three in use and one on standby. The pumps supplied a t omplex of pipes under the reactor that fed water to the separate pressure tubes. 

The two primary pumps with AC and DC pony motors flow 18,000 gpm of heavy water through the core for cooling. Following 60 MW operation, for 3 minutes, forced flow is needed to remove the decay heat. Upon loss of pony motors and primary pumps, forced flow is established through the shutdown cooling water system consisting of two pumps in parallel - one pump running and the other on standby. 

Pumps are operated in parallel to divide the load between two (or more) smaller pumps rather than a single large one, or to provide additional capacity in a system on short nodce, or for many other related reasons. Figure 3-35 illustrates the operational curve of two identical pumps in parallel, each pump handling one half the capacity at the system head conditions. In the parallel arrangement of two or more pumps of the same or different characteristic curves, the capacities of each pump are added, at the head of the system, to obtain the delivery flow of the pump system. Each pump does not have to carry the same How but it will operate on its own characteristic curve, and must deliver the required head. At a common tie point on the discharge of all the pumps, the head will be the same for each pump, regardless of its flow. 

Wien it is necessary to plan several pumps in parallel, the pump manufacturer must be advised, and care must be taken in arranging suction piping for the pumps, otherwise each may not carry its share of the flow. 

The quantity of liquid to be handled. This primarily affects the size of the pump and determines whether it is desirable to use a number of pumps in parallel. 

The sorption pumps are clean but are one shot , that is, two pumps in parallel and connected by valves alternatively are needed for a continuous pumping. When the first pump is saturated, the second pump is started, while the first is regenerated removing the liquid nitrogen, the trapped gas is expelled through the blow-off valve. The pump (with zeolite) is heated to 200-300°C to remove water vapour. Charcoal pumps are heated to about 100°C. 

Diskind (1959) determined the operating characteristics for centrifugal pumps in parallel and in series using a simple graphical method. 

Consider two centrifugal pumps in parallel as shown in Figure 4.9. The... 

The operating characteristics for two pumps in parallel are obtained as follows. 

Compare QT from Step 3 with Qs from Step 2. If they are not equal repeat Steps 2, 3 and 4 until QT = Qs. This is the operating point of the two pumps in parallel. 

An alternative to this trial and error procedure for two pumps in parallel is to calculate QT from equation 4.32 for various values of the total head from known values of Q and Q2 at these total heads. The operating point for stable operation is at the intersection of the AhT against QT curve with the A/ts against Qs curve. 

The problem at Big Spring was rather typical. The two parallel, second-stage jets were not working as a team. Jet A in Fig. 16.5 was a real strong worker. Jet B was a loafer. It is rather like running two centrifugal pumps in parallel. Unless both pumps can develop about the same feet of head, the strong pump takes all the flow, and the weak... 

Operating Points of Single and Double Pumps in Parallel and Series... 

Figure 7.17. Operating points of centrifugal pumps under a variety of conditions, (a) Operating points with a particular pump characteristic and system curves corresponding to various amounts of flow throttling with a control valve, (b) Operating point with two identical pumps in parallel each pump delivers one-half the flow and each has the same head, (c) Operating point with two identical pumps in series each pump delivers one-half the head and each has the same flow.

Another multisyringe FI separation system design has been used in the analysis of stable and radioactive Y, using an extraction-chromatographic material containing HDEHP adsorbed on a C18 support.123 Separated samples were analyzed off-line by ICP-AES and proportional counting. This system used four syringe pumps in parallel. 

Pump turndown and rangeability can be increased by operating two or more pumps in parallel. 

Dimensions of a Fluidized Bed Vessel 125 Application of Dimensionless Performance Curves 132 Operating Points of Single and Double Pumps in Parallel and Series 133... 

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