Flowserve Twin Screw Rotary - Manual (Page 47)

TWIN SCREW PUMPS. ORIGINAL USER INSTRUCTIONS. ENGLISH. 71569243 – 07/10
Page 44 of 53
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7 FAULTS; CAUSES AND REMEDIES
FAULT SYMPTOM
P u m p o v e r h e a t s a n d s e i z e s
⇓ ⇓ B e a r i n g s h a v e s h o r t l i f e
⇓ ⇓ P u m p v i b r a t e s o r i s n o i s y
⇓ ⇓ M e c h a n i c a l s e a l h a s s h o r t l i f e
⇓ ⇓ M e c h a n i c a l s e a l l e a k s e x c e s s i v e l y
⇓ ⇓ P u m p r e q u i r e s e x c e s s i v e p o w e r
⇓ ⇓ P u m p l o s e s p r i m e a f t e r s t a r t i n g
⇓ ⇓ I n s u f f i c i e n t p r e s s u r e d e v e l o p e d
⇓ ⇓ I n s u f f i c i e n t c a p a c i t y d e l i v e r e d
⇓ ⇓ P u m p d o e s n o t d e l i v e r l i q u i d
⇓ ⇓
PROBABLE CAUSES POSSIBLE REMEDIES
A. System troubles
z z Pump not primed.
z z z z
Pump or suction pipe not completely filled with
liquid.
Check complete filling. Vent and/or prime.
z z z z Suction lift too high or level too low.
z z z z
Insufficient margin between suction pressure and
vapour pressure.
Check NPSHa>NPSHr, proper submergence,
losses at strainers/fittings.
z z z Excessive amount of air or gas in liquid. Check and purge pipes and system.
z z z Air or vapour pocket in suction line. Check suction line design for vapour pockets.
z z Air leaks into suction line. Check suction pipe is airtight.
z z
Air leaks into pump through mechanical seal,
sleeve joints, casing joint or pipe plugs. Check and replace faulty parts.
CONSULT FLOWSERVE.
z z Foot valve too small. Investigate replacing the foot valve.
z z Foot valve partially clogged. Clean foot valve.
z z z z Inlet of suction pipe insufficiently submerged. Check out system design.
z z z Speed too low. CONSULT FLOWSERVE.
z Speed too high. CONSULT FLOWSERVE.
z z z
Total head of system higher than differential head
of pump.
z
Total head of system lower than pump design
head.
Check system losses.
Remedy or CONSULT FLOWSERVE.
z Specific gravity of liquid different from design.
z z z
Viscosity of liquid differs from that for which
designed.
Check and CONSULT FLOWSERVE.
z z
Operation at very low capacity. Measure value and check minimum permitted.
Remedy or CONSULT FLOWSERVE.
z z z
Operation at high capacity. Measure value and check maximum permitted.
Remedy or CONSULT FLOWSERVE.
B. Mechanical troubles
z z z z z z
Misalignment due to pipe strain. Check the flange connections and eliminate strains
using elastic couplings or a method permitted.
z
Improperly designed foundation. Check setting of baseplate: tighten, adjust, grout
base as required.
z z z z Rotating part rubbing on stationary part internally. Check and CONSULT FLOWSERVE, if necessary.