In practical operation of drilling fluid system there are single pump operation, duplicate pumps operation, pumps in parallel, pumps series operation. The difference is as below
Pumps duplicity
Two pumps can be configured in parallel but only one pump is operated at a time, thus providing a primary and a backup pump. The two pumps are separated by a valve in each discharge line that prevents one pump from pumping through the other. This type of configuration is perfectly acceptable and, in crucial applications, encouraged.
Parallel Operation
Parallel operation is discouraged for centrifugal pumps. If an applica- tion exists that requires high volume and low head and volume required is greater than can be produced by a single pump, two pumps are sometimes used in a parallel configuration to meet the demand. Two pumps that produce the same TDH can be configured so that each pump has an individual suction but both pumps feed into the same discharge line. If the pumps are identical, head in the discharge line is equal to that of the pumps, but the volume is double what a single pump can produce. However, two centrifugal pumps will never have the exact same discharge head, and as wear occurs one pump will produce less head than the other and the stronger pump will overpower the weaker pump and force fluid to backflow into the weaker pump. For this reason, parallel operation is not normally recommended.
Series operation on centrifugal pump
There are times when a single centrifugal pump will not meet the head requirements of an application. Two pumps can be operated in series to achieve the desired discharge head, in which the discharge of one pump feeds the suction of the second pump. The second pump boosts the head produced by the first. Therefore, if an application required 2900 gpm at 200 feet of head, one option would be to run two 10 8 14 pumps in series. Each pump could be configured with a 13-inch impeller to produce 2900 gpm at 100 feet of head. When operated in series, the pumps would produce 2900 gpm at 200 feet of head.
This type of configuration is most commonly used for extremely long discharge runs. When running pumps in series, it is important not to exceed flange safety ratings. Additionally, it is not required to place pumps within close proximity of each other. If an application had a 6-mile discharge line the first pump could be located at the supply source and the second pump could be located 3 miles away.
