Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 3 Western Australia, Series 3
Volume 3
Number 1 January-February, 1955 Article 10
1-1954
How to get the best results from centrifugal pumps How to get the best results from centrifugal pumps
H K. Gibsone
Department of Agriculture
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Recommended Citation Recommended Citation
Gibsone, H K. (1954) "How to get the best results from centrifugal pumps," Journal of the Department of Agriculture, Western Australia, Series 3: Vol. 3: No. 1, Article 10.
Available at: https://researchlibrary.agric.wa.gov.au/journal_agriculture3/vol3/iss1/10
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HOW TO GET THE BEST RESULTS FROM CENTRIFUGAL PUMPS
By H. K. GIBSONE, Officer-in-Charge, Irrigation Branch
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ANY thousands of centrifugal pumps are operating throughout the State, a n d from observations made while travelling around the country I find t h a t , like t h e wind- mill, the pump is very frequently a neglected piece of equipment. The following hints may assist users to get to obtain good results from their pumps. Most of t h e m are taken from a check list prepared by Mr. A. B. Lohr of the Engineering Department, Goulds Pumps Inc., New York.The centrifugal pump is a sturdy and dependable piece of machinery which sel- dom fails to perform satisfactorily pro- viding it is properly installed, adjusted, lubricated and operated within its rated capacity. The following pointers will help growers to get t h e best possible service from their pumps.
INSTALLATION
Where the pump is part of a permanent installation it should be properly set in on a concrete foundation and carefully levelled. When a flexible coupling is used, check the alignment with a feeler gauge and straight-edge.
I n the case of portable units the pump unit should be blocked so t h a t it is per- fectly level and cannot creep. The align- ment should be thoroughly checked each time the pump is operated.
All piping should be supported indepen- dently of the pump to relieve the machine of unnecessary strain. Suction piping should be as short and direct as possible, sloping upward from t h e supply to the pump. The suction lift should be not over 16ft. including the friction head. The suc- tion piping should be as large as the pump suction and, if more t h a n 20ft. long, a size larger, reducing a t the p u m p with a n eccentric reducer to avoid any air traps in the line.
All piping joints must be airtight and the discharge piping should be a t least as large as the p u m p discharge with as few fittings as are practicable.
The strainer should be installed a t least 3ft. below the lowest level in t h e water supply, and should be inspected and cleaned frequently to ensure t h a t it is free from foreign matter.
PRIMING
In the case of self-priming pumps the casing must be filled with water when started for the first time, after which they will prime themselves for future starts.
Those pumps which are not self-priming must be primed for the first s t a r t and t h e n the prime can be held by a foot-valve in the suction line. Such pumps should be checked before each start as the check valve or stuffing-box may leak, causing the pump to loose its priming.
The centrifugal pump shown In the photograph Is a simple single-stage pump of a popular type. It Is shown being electrically driven by a flat belt, but would be more efficient If a V-belt drive was used. Note that that suction and delivery pipes are attached to re- inforced rubber flexible hoses. The photograph also shows the solid concrete foundation which is essential
for these pumps
51
Motor-driven pumps are usually primed by pouring or pumping water by h a n d into t h e priming opening in t h e casing until water comes out of t h e open vent valve on top of t h e casing.
Engine-driven pumps are sometimes equipped with an exhaust primer. When using, be sure t h a t there is some water in t h e casing to lubricate the rotating p a r t s during t h e priming period.
Never r u n the p u m p unless it is fully primed.
When starting the unit during winter or during long off-periods, drain pump and remove the stuffing-box packing, grease the shaft and dry the p u m p thoroughly.
LUBRICATION
Motors with 'lubricated for life" bearings require no greasing, but other ball-bearing motors should be greased about every two or t h r e e m o n t h s . Do not over-grease, a n d consult t h e motor manufacturers' instruc- tion sheet if available.
T h e m a n u f a c t u r e r s ' instructions for oil- ing and greasing should be faithfully adhered to where petrol or kerosene e n - gines are used. The bearings of the p u m p should be lubricated according to t h e i n - struction sheet issued by t h e makers.
STUFFING-BOX
Where t h i s feature h a s a mechanical seal it requires no adjustment a n d should be repaired only by factory-trained men.
I n t h e case of packed stuffing-boxes, regular care is necessary a n d the gland should never be tightened so t h a t there is no leakage or so t h a t the box heats up in use. T h e stuffing-box should leak at least 40 to 60 drops per minute a n d the gland n u t s should be adjusted evenly and only finger-tight.
Where a grease lubricator is used give t h e h a n d l e a t u r n or two after about every h u n d r e d h o u r s ' operation.
PROTECTION OF EQUIPMENT Keep t h e pumping unit covered during wet weather. Disconnect all exposed elec- trical connections when not in use and instal suitable warning signs. In districts where heavy frosts are encountered, drain t h e p u m p a n d engine during freezing weather.
TROUBLE CHECK LIST 1. If not enough water is delivered.
(a) P u m p not completely primed.
(b) Speed too low.
(c) Suction lift too high.
(d) Discharge pressure too high.
(e) Impeller or suction pipe clogged.
(f) Air pockets in suction line.
(g) Stuffing-box packing worn or water seal plugged, allowing air to leak into the casing.
(h) Air leaks into suction line.
(i) Check valve installed incorrectly.
(j) Water supply too low.
(k) Strainer not submerged deeply enough.
(1) Impeller damaged.
(m) Casing gaskets defective.
2. Not enough Pressure.
(a) Speed too low.
(b) Air in water.
(c) Impeller damaged.
(d) Casing gaskets defective.
3. P u m p works for a while and then quits.
(a) Air leak in suction line.
(b) Stuffing-box packing worn.
(c). Air pocket in suction line.
(d) Suction lift too high.
4. P u m p leaks excessively a t stuffing-box.
(a) Packing is worn or not properly lubricated.
(b) Packing is not properly inserted or run in.
(c) Shaft or shaft sleeve is scored.
As a final note, I would like to remind users to make sure t h a t the pump is r o t a t - ing in the right direction as indicated by the arrow on t h e casing. Many beginner's troubles have stemmed from attempts to r u n the pump in the reverse direction to t h a t intended by t h e maker.
52
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