This article continues the series on pump installation and covers how the suction and discharge pipework should be installed, including baseplate mounting and the different types of bases.
Suction Pipework:
It is good practice to have the suction piping as short and straight as possible.
If practical, a straight length of 10 times the suction pipe diameter is recommended.
Sump Design – 1
Fig 1
Inadequate sump design leads to entrained air bubbles and turbulence, which will damage the pump.
Sump Design – 2
Fig 2
A submerged inflow pipe and tank baffles prevent turbulence and bubbles from entering the suction pipe.
Keep the suction pipe short and straight and eliminate all possibility of air pockets being trapped in the suction line, i.e., ensure the suction pipe rises continuously to the pump.
Fig 3
Air trapped in the suction system will reduce pump performance. Fig 4 illustrates where air can be trapped.
Fig 4
The diameter of the suction pipe is sized to suit the application and is often larger than the pump suction connection and provided with an eccentric taper which should be installed as shown in Fig 5.
Concentric – Not Recommended
Eccentric – Recommended
Fig 5
The correct distance between the inlet flange of the pump and the first elbow must be at least five pipe diameters.
Not recommended
Fig 6
Suction Strainers:
It is strongly recommended that suction strainers be installed in the suction line. For pumps drawing from rivers, dams, and open tanks, a suitable strainer should be installed at the start of the suction line to prevent debris that is too big from passing through easily.
In the case of a closed circuit system, which does not require a strainer because the fluid being pumped is clean, it is recommended that a temporary strainer be fitted in the suction line to prevent construction debris from clogging and damaging the pump. This strainer can be removed once the pump has been run for a few hours.
As a guide, all strainers should have a surface area at least three times the pipe diameter. For temporary strainers, the screen should be made of No.12 mesh and reinforced with No. 2 mesh and 12.6 mm wire. For all other strainers, the screen should be sized to stop solids larger than the pump can easily handle.
Discharge Pipework:
Install the discharge pipework according to the provided drawings or, if no drawings are available, according to proper industry practice. The common discharge arrangement consists of a pipe reducer, a non-return valve to prevent backflow when the pump is stationary, and an isolating valve for maintenance purposes. All these valves and pipework must be separately supported so that the pump casing does not bear their weight.
N.B. It is quite common for pumps to be fitted with flexible pipe connections on the suction and discharge, in conjunction with anti-vibration mounts under the baseplate. In this case, it is imperative that the pipework is correctly supported even when no anti-vibration mounts are fitted.
Pipe Expansion Joints:
When installing pipe expansion joints, ensure the following:
- The expansion joint must have the correct pressure rating for the application.
- When necessary, tie bolts will be needed to absorb the hydraulic loads in the discharge line from being transmitted to the pump set; if not, these loads can distort the baseplate.
Fig 7
Spring Mounts:
These are often used in conjunction with expansion joints.
Spring mounts are selected so that they deflect to half their deflection when the pump is mounted.
Seismic (restrained) anti-vibration mounts are required for earthquake zones. In accordance with the relevant standards). Some mining sites also specify them.
Baseplate Types:
Inertia
Skid
Skid-type baseplates are used for portable units, which are regularly moved around sites for ease of handling and are more robust than standard baseplates.
Pipework General
- All suction and discharge pipes and valves must be separately supported to prevent the pump from carrying their weight.
- If the pump is to be installed between fixed limits, it is recommended that it be temporarily connected to the pipes before it is grouted in.
- When connecting the pipes and pump, the pipes should be taken to the pump, not the pump to the pipes.
- Suction and discharge pipes should be firmly tightened after grouting is complete and before the final alignment check.
- If the unit is installed outdoors, care should be taken to ensure that extremes of ambient temperatures do not adversely affect the alignment.
The pump is installed on its foundation, grouted in and connected to the suction and discharge pipes and valves.
Summary
This article has continued the process of pump system installation such that the pump and its base and pipework are at a stage where they are almost ready for starting, and we will complete the process in the following articles on the alignment of the pump and driver, which is necessary before initial pump start-up.
