all about pumps part 2a

WHAT IS MEANT BY PUMP PRIMING???

Priming is a term used in pumps regarding their ability to draw-in liquid at the suction/ intake line without having much difficulty (as in using certain set-ups/ devices…)

Centrifugal pumps are non-priming which is why their suction lines necessitates the use of check valves/ foot valves…

Since there is a continuous passageway (even if not in operation) of the liquid inside, no liquid would be trapped assuming that there is no foot valve or that there is damage on the foot valve…

While reciprocating and rotary pumps due to their internal make-up has no continuous passageway, that there would only be if the pump is actuated.

As such, liquid is isolated thus not requiring any foot valve for isolation…

In cases that pumps warrants such condition (PRIMING) auxiliary priming instruments are needed to discharge liquid properly and at the soonest possible time….

TYPICAL AUXILIARY PRIMING METHODS:

Kinds of priming methods used in CPUMPS to take care of priming which could use extra/ additional devices/ equipments….

APM “A” uses a certain reservoir to help in priming where the natural effects of gravitation is used….

APM “B” uses a by-pass line coming from the discharge line….

APM “C” uses an auxiliary line to augment those trapped in the foot/ check valve…

APM “D” uses a separate pump used specifically to draw out air from the casing…

APM “E” uses an ejector to draw in liquid coming from the same source into the casing…

APM “F” uses a priming tank where due to its pressure conveys liquid into the pump before being diverted IN & OUT again…

APM “G” & “H” uses vacuum pumps that are either controlled manually or controlled automatically for pump priming…

MANUAL:

AUTOMATIC:

It is important to note that such means of APM also necessitates the proper use of valves & fittings…

IS PRIMING REQUIRED ALL THE TIME FOR CPUMPS???

YES

NO

YES…….If for the first time, the C-PUMP is to be operated…

NO…….If the C-PUMP has been previously operated with the foot valve properly working…

…… or if the installed foot valve is defective….

……or If the C-PUMP has suction head source or if the source is of the flooded type…

IN ALL POSSIBLE CIRCUMSTANCES, ARE RO-PUMPS & R-PUMPS SELF PRIMING???

YES

NO

YES……. for static lifts of only 28 ft…

NO…….If the static lift required is greater than 28 ft…

…… provided that there is no loss pressure in the inside (no damage)….

……or If there is certain degree of abrasion causing loss of pressure in the

inside…

WHAT IS MEANT BY PUMP CAVITATION???

Cavitation is a phenomena that is always associated with CPUMPS (as well as certain VALVE TYPES) in which there is formation of VAPOR BUBBLES/ VAPOR POCKETS within the pump casing…

This cavitation causes a DECREASE IN PUMP EFFICIENCY and worst PUMP FAILURE….

DETRIMENTAL EFFECTS

Cavitation begins as the formation of vapor bubbles at the impeller eye due to low pressure…

This formation is at the point where the lowest possible pressure of the pump could be located

At the point just prior to the liquid being acted upon by the impeller vanes…

Cavitation begins as the formation of vapor bubbles at the impeller eye due to low pressure…

Rapid impeller movement causes compression of vapor pockets to collapse (IMPLOSION) sending shockwaves inside the casing translating into vibration…

VAPOR BUBBLE FORMATION???

This vapor bubble formation is what we call “LIQUID VAPORIZATION” where liquid vaporizes into gas…

??? ARE WE FOOLING EACH OTHER AROUND???

Vaporization is synonymous to BOILING which is characterized by application of HEAT onto the substance (liquid)…

CORRECT?????? INCORRECT??????

However “BOILING/ VAPORIZATION OF LIQUID” is not only limited to such scenario…

Water boils at 100 oC or at 212 oF at SEA LEVEL or at locations slightly above….

REVIEW OF THERMODYNAMIC CONCEPT:

FACT # 1:

At high altitude locations, boiling point ofwater changes, in that they boil at a muchlower temperature….

FACT # 2:

FACT # 3: As such it would also be quicker to cook foods….

FACT # 3:

MISCONCEPTION:

It takes quite a longer time to cook foods***….

There are two ways to boil a liquid….

VAPOR PRESSURE & CAVITATION:

1. Increase the temperature of the liquid while keepingthe surrounding pressure constant***

*** rate of vaporization could be enhanced by also increasing the pressure surrounding/ accompanying such liquid (kettles & pressure cookers)…

2. Maintain the temperature while decreasing thepressure***

SEA LEVEL..t1 t2 t3 t4

100 oC/ 212 oF

P = 1 atmTemperature increases

VAPOR PRESSURE VS. TEMPERATURE:

SEA LEVEL..

P2

P3

t = 90 oC

P = 1 atmPressure

decreases

HIGH ALTITUDE..P = 70.14 kPA

P1

VAPOR PRESSURE VS. TEMPERATURE:

To make the liquid “BOIL” or “VAPORIZE”, a vacuum source is needed…

“TEMPERATURE CHANGE CORRESPONDS TO A CHANGE IN VAPOR PRESSURE…”

AGAIN WHAT IS MEANT BY PUMP CAVITATION???

A phenomena where there is formation of VAPOR BUBBLES/ VAPOR POCKETS within the CPUMP casing…

This happens because the pressure (region) inside the pump falls below the vapor pressure (saturation pressure) of the liquid…

SATURATION PRESSURE:

Necessary pressure for liquids to start its boiling…

Necessary pressure for gases to start its condensation…

As liquid enters the pump casing, it encounters a decrease in pressure…

As such the vapor pressure of the liquid is now greater than the inside pump pressure…

The liquid now starts to vaporize emitting liquid vapors…

This liquid vapor mixes with the other portions of liquid translating into BUBBLE FORMATION…

1. NOISE AND VIBRATION

WHAT ARE THE SIGNS/ SYMPTOMS OF CAVITATION…

2. DROP IN PUMP CAPACITY & EFFICIENCY

3. IMPELLER VANE CORROSION & PITTING

1. NOISE AND VIBRATION:

Low level cavitation in pumps are inaudible but higher levels produce varying distinctive sounds. And these maybe either any of the following:

1. Crackling or sizzling…2. Small steel object rapidly striking against a metal…3. Hissing, rushing, swishing, or a static like sound

similar to radio or television static.4. Suction Cavitation can produce loud knocking,

hammering, or crackling sounds, that are distinctive from discharge recirculation cavitation.

This noise is actually the sound produced as the vapor bubbles collapses as they are hit by the high speed impeller or as in the case of the hissing/ static television sound as there is no liquid sucked by the pump…

Vibration on the other hand takes place as the vanes hit “void/ empty space” (collapsed vapor bubble portion) whose empty space is suddenly taken by the surrounding liquid…

COULD THE SOUND OF CAVITATION BE DISTINGUISHED FROM OTHERS???

Experienced persons may be able to diagnose cavitation by its unique sound qualities. Cavity collapse has specific sound qualities that distinguish cavitation from sounds made by entrained gas bubbles, and also from the sound of failed bearings and other machinery noises.

1. A “TRAINED EAR” is capable of distinguishing IF or IF NOT.

2. Such sounds can start and stop quickly in response to changes in flow rate.

3. Such sounds exhibit precise repeatability, the noise is always the same under identical conditions.

.

SUPPOSEDLY THAT ENTRAINED BUBBLES TOOK THE PLACE OF VAPOR BUBBLES, HOW ARE THEY DISTINGUISHED???

Entrained gas bubbles moving through a pump or valve, make a softer and lower frequency sound than cavitation because of the immense difference in energy levels...

Sound from entrained gasses changes slowly to variations in flow rate, whereas, cavitation sounds appear and disappear quickly in response to small changes in flow rate, and sounds caused by cavitation have precise repeatability…

2. DROP IN CAPACITY & EFFICIENCY

With formation of vapor bubbles taking away certain spaces/ volumes, it would translate into a dip of its rated capacity (discharge)…

A dip in its capacity (discharge) means that there is less work/ lesser output given-off by the pump as supposed to its rated capacity thereby resulting into a decrease in its efficiency…

3. IMPELLER VANE CORROSION & PITTING

As the vapor bubbles collapses, the surrounding liquid rushes into that collapsed void space ACTING LIKE A CHISEL CUTTING AWAY AT A METAL resulting in a PITTING like manner, that of SLOWLY CHIPPING AWAY at the impeller vanes and at certain inner portions of the CPUMP casing…

That as bubble formation and collapse ensue, oxygen is liberated resulting into oxidation of the invlolved parts…

IMPELLER VANE CAVITATION PICTURES:

Suction cavitation specifically damaging the suction side of the vane and outer vane surfaces…

Such cavitation damage would only mean that large “cavities” had formed even before it had reached the impeller, thus damage is before the impeller…

IMPELLER VANE CAVITATION PICTURES:

Severe discharge recirculation cavitation specifically damaging the vane tips and outer ends of the front and rear shrouds…

Such cavitation damage indicates that the cavities had formed at the impeller portion thus damage is after passage…

CASING CAVITATION PICTURES:

CASING CAVITATION PICTURES:

IF IMPELLER IS AT THE DISADVANTAGE, HOW COULD THEY WITHSTAND SUCH PHENOMENA???

There are a variety of ways/ means to offset or at least minimize the destructive effects of such phenomena and one of them is the proper selection of the impeller/ casing material…

Metals normally have this protective layer (oxide layer) that protects them from corrosion…

Cavitation however continuously degrades such “layer” thereby further exposing them to oxidation… From then on, cavitation & corrosion work hand in hand to continuosly remove metal from the casing & impeller…

These would eventually lead to a wear and tear on the part of impeller & casing, leading to this probable condition…

No known material can withstand such phenomena but proper material selection can result in longer casing/ impeller life, that is why pump construction should be properly be analyzed…

In instances where pumps are not subjected to cavitation, or not predicted to be a problem, materials such as CAST-IRON & BRONZE can with-stand 20 or more years of service life…

The Materials listed below are in the order of their ability to withstand the undesirable effects of Cavitation:

1. Cast iron -- least resistance…2. Leaded Bronze…3. Cast carbon steel…4. Manganese bronze…5. Monel…6. Stainless steel…7. Cast nickel aluminum bronze…8. Titanium…9. Cast Carburized 12% Chromium Stainless, Chrome-manganese austenitic Stainless…

10. Stellite -- highest resistance…

Also an innovation in technology is used, in that SPECIAL POLYMERIC REBUILDING & COATING MATERIALS is used…

A special blend of polymeric material that reduces friction and improving its capability against wear and tear…

This is used not only in impellers but also for the casing. And is applied specifically onto damaged portions or portions prone to damage…

WHAT ARE THE POSSIBLE REASONS FOR PUMP CAVITATION???

Cavitation an undesired phenomena could be caused by any or a combination of any of the following:

1. Suction lift or Suction heads are lower than the manufacturer’s required parameters… 2. Speed (PRIME MOVER) is higher than the manufacturer’s required parameters… 3. Improper recognition of VAPOR PRESSURE/ TEMPERATURE of liquid conveyed (too high)…

4. Proper NPSHA (NET POSITIVE SUCTION HEAD AVAILABLE which is the required head at the pump inlet (suction) to prevent cavitation from forming…

C-PUMP ADVANTAGES….1. Ability to maintain a UNIFORM FLOW…

2. Small space requirement…

3. Low initial cost…

4. As compared to R-PUMPS, it could handle solids laden liquids without much difficulty but cannot compare to that of ROTARY TYPES…

5. Can handle/ convey large volume flow rates…

6. Foundation is much lighter…

7. Application of an E-MOTOR drive is possible…

C-PUMP DISADVANTAGES….1. Being a high speed machine, it is difficult to operate at

low speeds……

2. Not suitable for HIGH HEAD (TDH) requirements…

3. Not suitable at low flow rates…

4. It must be PRIMED before it can deliver liquids…

5. Being a high-speed machine, care is ncessary for the proper alignment of shafts…

6. Difficult to regulate with wide flunctuations in loads…

7. Have a lower efficiency as compared to R-PUMPS…

R-PUMP ADVANTAGES….

1. Able to start without priming

2. Have higher efficiencies as compared to CPUMPS in that they have a constant efficiency with variations in capacity and head…

3. It can pump small volumes of liquid at a desired head…

R-PUMP DISADVANTAGES….1. Greater floor space is required……

2. Higher in initial cost…

3. Costly design to construct in special alloys…

4. Rubbing contact is too high, so reciprocating part is difficult to seal against leakage…

5. Pulsating flow…

6. Not generally suitable for dirt or abrasive laden liquids…

7. Most types need protection against over pressure and over power due to its “energy impartment”…

Centrifugal pumps being the most commonly used type of pump because of its versatility and adaptability of usage requires an experienced personnel to properly maintain its proper workability..

They operate non-stop and their set-up necessitates the use of a back-up line should one falter…

C-PUMP TROUBLE SHOOTING GUIDE….1. PUMP DOES NOT DELIVER WATER/ LIQUID……

-- No power in prime mover…

-- Suction lift is too high or suction head is too low…

-- Speed is too low…-- Actual TDH is higher than computed TDH…-- Pump seizure/ damage…

-- Excessive amount of air or gas in liquid at the suction line (source)…

-- Improper use of foot valve/ damaged/ clogged foot valve…-- End of suction line insufficiently/ not submerged

at all…

-- Pump is not primed at all…

C-PUMP TROUBLE SHOOTING GUIDE….2. INSUFFICIENT CAPACITY DELIVERED……

-- Pump is not primed properly…-- Insufficient margin between suction pressure & vapor pressure…-- Excessive amount of air or gas in liquid at the suction

line (source)…-- Air leaks (seeping) into suction line…-- Air leaks into the pump thru the stuffing box…-- Improper use of foot valve/ damaged/ clogged foot valve…

-- Speed is too high…

-- Seal gauge improperly located in stuffing box preventing sealing liquid entering space to form a

“SEAL”…

C-PUMP TROUBLE SHOOTING GUIDE….2. INSUFFICIENT CAPACITY DELIVERED……

-- Viscosity of liquid different different from design criteria…

-- Wearing rings are worn…-- Impeller damage…

-- Foreign matter in the impeller…

-- Casing gasket is defective allowing liquid leakage…

-- Packing improperly installed…

-- Incorrect type of packing for operating conditions…

-- Actual TDH is equal to computed TDH…

C-PUMP TROUBLE SHOOTING GUIDE….3. PUMP LOSES PRIME AFTER STARTING……

-- Pump is not primed properly…

-- Seal gauge improperly located in stuffing box preventing sealing liquid entering space to form a

“SEAL”…

-- Excessive amount of air or gas in liquid at the suction line (source)…

-- Air leaks in suction line…-- Air leaks into the pump thru the stuffing box…

-- End of suction line insufficiently/ not submerged …

-- Improper use of foot valve/ damaged/ clogged foot valve…

C-PUMP TROUBLE SHOOTING GUIDE….4. STUFFING BOX LEAKS PROFUSELY……

-- Seal gauge improperly located in stuffing box…

-- Worn bearing…

-- Shaft misalignment…

-- Packing improperly installed…

-- Motor rotor imbalance…-- Incorrect type of packing for operating conditions…

-- Bent shaft…

-- Improper bearing installation…-- Machine foundation with CPUMP set-up not rigid…-- Impeller damage…

C-PUMP TROUBLE SHOOTING GUIDE….4. STUFFING BOX LEAKS PROFUSELY……

-- Dirt or grit in bypass line wearing/ scoring the shaft/ shaft sleeve…-- Excessive thrust due to sudden surge in electricty…-- Lack of grease/ oil lubrication in oil chamber causing

bearing overheating…-- Dirt or grit in bypass line contaminating the

packing material…

-- Water seeping into oil chamber…

-- Bypass line to seal gauge not working…

C-PUMP TROUBLE SHOOTING GUIDE….5. PACKING HAS A SHORT LIFE THAN EXPECTED…..

-- Seal gauge improperly located in stuffing box…

-- Bent shaft…

-- Improper bearing installation…

-- Shaft misalignment…

-- Machine foundation with CPUMP set-up not rigid…

-- Worn bearing…

-- Foreign matter in the impeller…

-- Impeller damage…-- Packing improperly installed…-- Incorrect type of packing for operating conditions…

C-PUMP TROUBLE SHOOTING GUIDE….5. PACKING HAS A SHORT LIFE THAN EXPECTED…..

-- Motor rotor imbalance…-- Gland is too tight…-- Bypass line to seal gauge not working…-- Dirt or grit in bypass line contaminating the

packing material…-- Excessive thrust due to sudden surge in electricty…-- Lack of grease/ oil lubrication in oil chamber causing

bearing overheating…-- Dirt accumulating in bearing…-- Water seeping into oil chamber…

C-PUMP TROUBLE SHOOTING GUIDE….6. PUMP VIBRATES OR IS TOO NOISY……

-- Pump is not primed at all…

-- Insufficient margin between suction pressure & vapor pressure…

-- Improper use of foot valve/ damaged/ clogged foot valve…-- End of suction line insufficiently/ not submerged…-- Foreign matter in the impeller…

-- Pump is not primed properly…

-- Air leaks (seeping) into suction line…-- Air leaks into the pump thru the stuffing box…

-- Shaft misalignment…-- Shaft is bent…

C-PUMP TROUBLE SHOOTING GUIDE….6. PUMP VIBRATES OR IS TOO NOISY……

-- Worn bearing…

-- Excessive thrust due to sudden surge in electricty…-- Motor rotor imbalance…

-- Excessive grease/ oil lubrication in oil chamber…-- Lack of grease/ oil lubrication in oil chamber causing

bearing overheating…

-- Shaft sleeve/ shaft worn at packing portion…

-- Water seeping into oil chamber…

-- Improper bearing installation…-- Machine foundation with CPUMP set-up not rigid…-- Impeller damage…

-- Dirt accumulating in bearing…

C-PUMP TROUBLE SHOOTING GUIDE….7. BEARINGS HAVE SHORT LIFE…

-- Machine foundation with CPUMP set-up not rigid…

-- Excessive thrust due to sudden surge in electricty…

-- Dirt accumulating in bearing…-- Water seeping into oil chamber…

-- Lack of grease/ oil lubrication in oil chamber causing bearing overheating…

-- Shaft misalignment…-- Shaft is bent…

-- Motor rotor imbalance…

-- Improper bearing installation…

-- Foreign matter in the impeller…

-- Impeller damage…

C-PUMP TROUBLE SHOOTING GUIDE….8. PUMP OVERHEATS THEN SEIZES…

-- Shaft is bent…-- Shaft misalignment…

-- Pump is not primed at all…

-- Worn bearing…

-- Insufficient margin between suction pressure & vapor pressure…

-- Operation is at very low capacity…

-- End of suction line insufficiently/ not submerged at all…

-- Foreign matter in the impeller…

-- Improper bearing installation…

C-PUMP TROUBLE SHOOTING GUIDE….8. PUMP OVERHEATS THEN SEIZES…

-- Motor rotor imbalance…

-- Excessive thrust due to sudden surge in electricty…

-- Dirt accumulating in bearing…-- Water seeping into oil chamber…

-- Lack of grease/ oil lubrication in oil chamber causing bearing overheating…

-- Machine foundation with CPUMP set-up not rigid…