PUMPS - TYPES & OPERATION - Advantages & Disadvantages of Piston Pumps
Written by Norrie
Saturday, 27 March 2010 14:10
Page 17 of 17
Some Advantages of Piston Pumps
- Reciprocating pumps will deliver fluid at high pressure (High Delivery Head).
- They are 'Self-priming' - No need to fill the cylinders before starting.
Some Disadvantages of Piston Pumps
- Reciprocating pumps give a pulsating flow.
- The suction stroke is difficult when pumping viscous liquids.
- The cost of producing piston pumps is high. This is due to the very accurate sizes of the cylinders and pistons. Also, the gearing needed to convert the rotation of the drive motor into a reciprocating action involves extra equipment and cost.
- The close fitting moving parts cause maintenance problems, especially when the pump is handling fluids containing suspended solids, as the particles can get into the small clearances and cause severe wear. The piston pump therefore, should not be used for slurries.
- They give low volume rates of flow compared to other types of pump.
A single acting pump with One cylinder is called a ' Single-acting Simplex ' pump.
A double acting pump with One cylinder is called a ' Double-acting Simplex '.
Where more than one cylinder is being driven by one driver, the arrangement is named according to the type and number of cylinders.
- A Single-acting Duplex pump has TWO single acting cylinders.
- A Double-acting Duplex pump has TWO double acting cylinders.
- A Single-acting Triplex pump has THREE single acting cylinders.
- A ' Double-acting Triplex ' pump has THREE double acting cylinders.
The more double-acting cylinders in a pump arrangement, driven by a single motor, the smoother and pulsation-free, is the output.
CONVERTING ROTATION INTO RECIPROCATION
The electric motor drives a fly-wheel or cam-shaft which is connected eccentrically to a connecting rod. The other end of the connecting rod is coupled to a 'Cross-head Gear' and 'Slide Assembly'. (This arrangement is the basis of the operation of the old Steam Engine drive cylinders and pistons).
As the motor rotates the fly-wheel or cam, the eccentrically mounted connecting rod rotates with it. This causes the rod to move up and down and backwards and forwards. The up and down motion cannot be transmitted to the pump shaft - it would not work. We do however, need the back and forth movement.
The connecting rod goes to the cross-head gear which consists of a pivot inserted into the slide assembly. The pivot removes the up and down movement of the rod but allows the pump shaft to move back and forth.
The diagrams will explain the principle much more easily than words.
( See following Figures : 32, 33)
ROTATION TO RECIPROCATION
Figure : 32
CONVERSION FROM ROTATION TO RECIPROCATION
Last Updated on Saturday, 27 March 2010 15:27