1.1 Auxiliary pump equipment, installation and maintenance

Auxiliary pump equipment, installation and maintenance

In addition to the pump unit itself, auxiliary pump equipment, installation and maintenance often require a fairly extensive consideration before commissioning. Guidance and instructions on this subject are given below.

With the exception of pumps directly incorporated into the piping, as well as submersible pumps and builders’ drainage pumps, a pump requires a foundation. This may be of concrete or designed as a steel structure. In the case of large pumps thorough strength of  materials calculations must usually be carried out. The dimensioning is executed in accordance with the pump supplier’s measurement drawings and other information. To the foundation bolt centre line dimensions adequate space should be added for their  fastening. If the type of pump in question requires free space in the axial direction beyond the shaft journal at the driving end, this dimension is also added. Further, the foundation should be sufficiently high to facilitate the connection of pipes and to ensure adequate space for drainage devices, if any, and that there is space for the fitting and maintenance of filters in the connection pipes.

The purpose of the foundation is that, by virtue of its mass, it is capable of counteracting vibrations and absorbing external loads such as hydraulic loads and tightening forces from pipes as well as to preserve the pump-motor alignment. If low noise-level demands are imposed, the foundation may have to be of a special vibration-suppressing design.

Horizontal pumps are usually supplied with pump and motor mounted on a common base plate of cast iron or frame construction, tested and aligned. Large pumps are generally supplied with a separate motor. Alignment in such cases requires more extensive work and must be performed on the foundation.

Vertical pumps with attached motors are supplied with a base or mounting plate, tested and aligned. In the dimensioning of foundations regard must be paid to the relationship between the height of the pump and the surface of the base or mounting- plate as well as to the torsional moment of the pump unit. If the pump unit is divided, for example, so that the electric motor can be mounted above an overflow level, separate foundations must be designed for both the motor and the pump.

Equipment in pipe systems

Valves of various types must normally be installed in the pipe system associated with the pump. When choosing these, allowance must be made for the loss of pressure which always takes place. The difference in this respect between various kinds of valves  intended for the same application can be considerable. Information on this subject should be requested from possible supplies and studied. See also Chapter 9, Pump System.

Manually operated shut-off valves with position indicators, e.g. with an ascending spindle, are suitable for use when it is necessary to rapidly establish the position of the valve. In the case of larger sizes geared types of valve are necessary.

Non-return valves of flap type with external levers are often of practical use. In this way it is possible to achieve functional control in addition to being able to open the valve manually. The disadvantage is difficulty in efficiently sealing the shaft bushing to the  external lever. Non-return valves should be provided with inspection covers so that the operation can be tested and flaps and balls replaced without dismantling the valve. If a non-return valve is required for the system, it should be located between the pump and a  shut-off valve, so that it is not necessary to drain the delivery pipe when repairing the non-return valve. When pumps are operating in parallel, the delivery pipe of every pump must have its own non-return valve so that one pump cannot pump backwards through another.

When pneumatically or hydraulically operated valves are used, a special operating and control system is required for the purpose. This can be relatively complicated. As a rule electrically controlled solenoid valves of small dimensions are used in systems of this kind. It is usually necessary to insist on comparatively clean operating media in such cases to avoid the risk of blockages and subsequent functional defects. If pneumatic or hydraulic valves must close in the event of pump stoppage caused by an electrical power failure, the operating medium must be independent of the electric circuit. This generally means the incorporation of an air vessel or a hydrophore.

Valves operated by electric motors are relatively expensive, but afford very good possibilities of regulation. Naturally they do not function in the event of a power failure. If throttle regulation is applied by means of a valve, the throttle valve must always be located in the delivery pipe. Valves in the suction pipe must only be used for shut-off. They should be of a type permitting unimpeded flow to ensure the minimum losses and undisturbed flow into the pump. Seat type valves must not be installed in a suction pipe immediately before a pump. See figure 1.1a & b Valves in suction pipes.

Relief valves are used in displacement pumps to prevent harmful increases of pressure in the event of the delivery pipe becoming temporarily blocked. Relief valves, which are often directly built into the pump, should not be used for the regulation of flow.

Direct connection between suction and delivery pipes in displacement pumps can give rise to increases in temperature in the event of marked rises in pressure or greatly increased flow. In the case of the pumping of oil, this means a reduction of viscosity and a risk of a defective oil film which could result in the pump seizing up. Instead, the liquid should be led directly back from the relief valve to a tank or similar vessel, where a larger volume can absorb the rise in temperature.

In the suction side of pumps screens or filters of various kinds may be necessary to prevent blockage or to provide protection against objects which can cause damage. These must be accessible for cleaning or replacement. The loss of pressure in filters and screens must be noted as this increases  with the degree of blockage. It may be necessary to install manometers in front of or behind screens to check conditions. Standard screens are designated by width of mesh or diameter of holes as well as number of meshes or holes per unit of surface. For this purpose there are international standards.

See figure 10.2.

Pump sumps for water containing sand should be equipped with a sand and grave/ trap, in which the rate of flow should be reduced to about 0.3 m/s so that sedimentation may take place. Sand traps of this kind must be emptied at suitable intervals if they are to function efficiently.

Pumping stations for sewage are sometimes provided with grills to trap rags, pieces of wood, etc. and thereby prevent blockage of the pumps. The cleaning of these grills is a complicated process and is usually carried out by mechanical means in large-scale systems. Reverse flushing through the pump during every shut down period can reduce the risk of blockage considerably. If the delivery pipe is very short, its entire volume can be used for reverse flushing; in other cases an arrangement of valves is also effective.