Lifting From Open Water

Question 1

Primers - function

Answer 1

The function of a primer is to remove air from the pump and create a partial vacuum

Question 2

Primers

There are three ways to prime a centrifugal pump:

Answer 2

• Use a gravity fed supply (on-board tank)
• Use a pressure fed supply (hydrant or another pumping appliance)
• By using a priming device to remove the air from the pump

Question 3

Priming

Answer 3

• The air in the hard suction and pump casing must be expelled so that atmospheric pressure will force water into the pump.
• Water ring primer
• Reciprocating primer
• Exhaust gas ejector

Question 4

Lifting from open water

Depth and atmospheric pressure pushing down

Answer 4

8m and approx 1 bar of pressure

Question 5

Lifting from open water

Answer 5

• The height to which water can be lifted is referred to as head
  • The maximum practical lift is generally considered to be 8 meters.

This is the distance measured from the eye of the pump to the surface of the water source.
• The maximum theoretical lift is 10 metres which equates to 1 bar of atmospheric pressure.

Question 6

Practical Limitations of Lifting From Open Water

Factors affecting:

CRESTA

Answer 6

• Creating the flow
• Resistance from suction hose and couplings
• Entry loss as the water enters the pump
• Strainer
• Temperature
• Atmospheric pressure

Question 7

Compound Gauge

Answer 7

Records a negative pressure when working from an open source and a positive pressure when working from a pressure fed supply

Question 8

Working From Open Water

Pump fails to achieve a prime

Answer 8

If the pump fails to prime, the compound gauge will show either no vacuum reading or a very high vacuum reading.

Question 9

Working from open water

No vacuum reading:

Answer 9

• The strainer may not be adequately submerged
• Loose or faulty suction hose joints
• An open drain cock, or loose drain plug in the pump casing
• Delivery valves not seating properly.
• Air leaks in the suction hose
• Defective seal
• A serious leak in one of the pipes leading to the gauges.

Question 10

Working from Open Water

Very high vacuum reading:

Answer 10

• A blockage around the strainer
• Faulty suction hose (the hose may have collapsed, or the internal lining may have come apart)
• Strainer sinking into mud or debris.

Question 11

Working from Open Water

Complete loss of a vacuum reading may be caused by:

Answer 11

• Strainer rising too near to the surface
• Water level has dropped too low

In either case, plenty of warning would be given to the pump operator by fluctuation in gauge readings and possibly engine speed.

Question 12

Working From Open Water

Decreased vacuum reading may be caused by:

Answer 12

• Branches being closed
• The water supply level rising (tidal etc.)
• Slight leak on the suction side of the pump.

Question 13

Working From Open Water

Increased vacuum reading may be caused by:

Answer 13

• Branches being opened
• The water supply level has dropped (tidal etc.)
• Strainer partially or completely blocked
• Burst length of delivery hose.