Vertical Turbine Pumps

Pump Application Data

1. DATUM OR GRADE - The elevation of the surface from which the pump is supported.

2. STATIC LIQUID LEVEL - The vertical distance from grade to the liquid level when no liquid is being drawn from the well or source.

3. DRAWDOWN - The distance between the static liquid level and the liquid level when pumping at required capacity.

4. PUMPING LIQUID LEVEL - The vertical distance from grade to liquid level when pumping at rated cap-acity. Pumping liquid level equals static water level plus drawdown.

5. SETTING - The distance from grade to the top of the pump bowl assembly.

6. TPL (TOTAL PUMP LENGTH) - The distance from grade to lowest point of pump.

7. RATED PUMP HEAD - Lift below discharge plus head above discharge plus friction losses in discharge line. This is the head for which the customer is responsible and does not include any losses within the pump.

8. COLUMN AND DISCHARGE HEAD FRICTION LOSS - Head loss in the pump due to friction in the column assembly and discharge head. Friction loss is measured in feet and is dependent upon column size, shaft size, setting, and discharge head size. Values given in appropriate charts in Data Section.

9. BOWL HEAD - Total head which the pump bowl assembly will deliver at the rated capacity. This is curve performance.

10. BOWL EFFICIENCY- The efficiency of the bowl unit only. This value is read directly from the performance curve.

11. BOWL HORSEPOWER- The horsepower - required by the bowls only to deliver a specified capacity against bowl head.

12. TOTAL PUMP HEAD - Rated pump head plus column and discharge head loss. Note: This is new or final bowl head.

13. SHAFT FRICTION LOSS - The horsepower required to turn the lineshaft in the bearings. These values are given in appropriate table in Data Section.

14. PUMP BRAKE HORSEPOWER - Sum of 'bowl horsepower plus shaft loss (and the driver thrust bearing loss under certain conditions).

15. TOTAL PUMP EFFICIENCY (WATER TO WATER) -The efficiency of the complete pump less.the driver, with all pump losses taken into account.

16. OVERALL EFFICIENCY (WIRE TO WATER)-The efficiency of the pump and motor complete. Overall efficiency = total pump efficiency X motor efficiency.

17. SUBMERGENCE-Distance from liquid level to suction bell.

Vibration Analysis

Vibration analysis equipment enables you to tell when "normal" vibration becomes "problem" vibration or exceeds acceptable levels. It may also allow you to determine the source and cause of the vibration, thus becoming an effective preventive maintenance and troubleshooting aid.

A vibration analyser measures the amplitude, frequency and phase of vibration. Also when vibration occurs at several frequencies, it separates one frequency from another so that each individual vibra-tion characteristic can be measured.

The vibration pickup senses the velocity of the vibration and converts it into an electrical signal. The analyzer receives this signal, converting it to the corresponding amplitude and frequency.

The amplitude is measured in terms of peak-to-peak displacement in mils (1 mil = .001") and is indicated on the amplitude meter.

Some instruments are equipped with a frequency meter which gives a direct readout of the predominant frequency of the vibration. Other instruments have tunable filters which allow scanning the frequency scale and reading amplitude at any particular frequency, all others being filtered out.

A strob light is used to determine the phase of vibration. It can be made to flash at the frequency of the vibration present or at any arbitrary frequency set on an internal oscillator.

A reference mark on a rotating part viewed under the strob light flashing at the vibration frequency may appear as a single frozen (or rotat-ing) mark, or as several frozen (or rotating) marks. The number of marks viewed is useful in determining the source of the vibration. The location of the mark or marks is used in balancing rotating parts.

The first step in vibration analysis is to determine the severity of the vibration, then, if the vibration is serious, a complete set of vibration readings should be taken before attempting to analyze the cause. Fig. 1 is the typical guide for end suction stock pumps as published by the Hydraulic Institute. The amplitudes shown are the overall RMS obtained without filtering to specific frequencies. Amplitudes at specific frequencies, such as vane pass frequency with multi-vane impellers, should be less than 75% of the unfiltered amplitudes allowed in Fig. 1 at the operating RPM. For other pumps, refer to Hydraulic Institute standards or pump manufacturer.

Fig. 1 Acceptable Field Vibration Limits for Horizontal Pumps - Clear Liquid (Rigid Structures)

Severity of vibration is a function of amplitude and pump speed; however, it should be noted that a change in severity over a period of time is usually a warning of impending failure. This change is often more important than vibration in the "slightly rough" or "rough" ranges which does not change with time.

Complete pump vibration analysis requires taking vibration readings at each bearing in three planes (horizontal, vertical and axial). Readings at the pump suction and discharge flanges may also be useful in some cases.

Field Testing Methods 2

e.)OrificeAn orifice is a thin plate containing an opening of specific shape and dimensions. The plate is installed in a pipe and the flow is a function of the pressure upstream of the orifice. There are numerous types of orifices available and their descriptions and applications are covered in the Hydraulic Institute Standards and the ASME Fluid Meters Report. Orifices are not recommended for permanent installations due to the inherent high head loss across the plate.

Fig. 6 Weirs

f.) Weir

A weir is particularly well suited to measuring flows in open conduits and can be adapted to extremely large capacity systems. For best accuracy, a weir should be calibrated in place. However, when this is impractical, there are formulas which can be used for the various weir configurations. The most common types are the rectangular contracted weir and the 90 V-notch weir. These are shown in Fig. 6 with the applicable flow formulas.

g.) Pitot tube

A pilot tube measures fluid velocity. A small tube placed in the flow stream gives two pressure readings: one receiving the full impact of the flowing stream reads static head + velocity head, and the other reads the static head only (Fig. 7). The difference between the two readings is the velocity head. The velocity and the flow are then determined from the following well known formulas.

Capacity = Area x Average Velocity

Since the velocity varies across the pipe, it is necessary to obtain a velocity profile to determine the average velocity. This involves some error, but when properly applied a calibrated pilot tube is within plus or minus 2% accuracy.

Fig. 7 Pitot Tube

Measurement of capacity

Measurement of capacity

a.) Magnetic Flow Meter

A calibrated magnetic flow meter is an accurate means of measuring flow in a pumping system. However, due to the ex-pense involved, magnetic flow meters are only practical in small factory test loops and in certain process pumping systems where flow is critical.

b.) Volumetric measurement

Pump capacity can be determined by weighing the liquid pumped or measuring its volume in a calibrated vessel. This is often practical when pumping into an accurately measured reservoir or tank, or when it is possible to use small containers which can be accurately weighed. These methods, however, are normally suited only to relatively small capacity systems.

c.) Venturi meter

A venturi meter consists of a converging section, a short con-stricting throat section and then a diverging section. The object is to accelerate the fluid and temporarily lower its static pressure. The flow is then a function of the pressure differential between the full diameter line and the throat. Fig. 4 shows the general shape and flow equation. The meter coefficient is determined by actual calibration by the manufacturer and when properly installed the Venturi meter is accurate to within plus or minus 1%.

Fig. 4 Venturi Meter

d.) Nozzle

A nozzle is simply the converging portion of a venturi tube with the liquid exiting to the atmosphere. Therefore, the same formula can be used with the differential head equal to the gauge read-ing ahead of the nozzle. Fig. 5 lists theoretical nozzle discharge flows.

Field Testing Methods

A. Determination of total head
The total head of a pump can be determined by gauge readings as illustrated in Fig. 1.

Fig 1 Determination of Total Head from Guage Readings

Negative Suction Pressure:
TDH = Discharge gauge reading converted to feet of liquid + vacuum gauge reading converted to feet of liquid + distance between point of attachment of vacuum gauge and the centerline of the discharge

Positive Suction Pressure:
or TDH=Discharge gauge reading converted to feet of liquid-pressure gauge reading in suction line converted to ft. of liquid + distance between center of discharge and suction gauges, h, in feet

In using gauges when the pressure is positive or above atmos-pheric pressure, any air in the gauge line should be vented off by loosening the gauge until liquid appears. This assures that the entire gauge line is filled with liquid and thus the gauge will read the pressure at the elevation of the centerline of the gauge. However, the gauge line will be empty of liquid when measuring vacuum and the gauge will read the vacuum at the elevation of the point of attachment of the gauge line to the pipe line. These assumptions are reflected in the above definitions.

The final term in the above definitions accounts for a difference in size between the suction and discharge lines. The discharge line is normally smaller than the suction line and thus the dis-charge velocity is higher. A higher velocity results in a lower pressure since the sum of the pressure head and velocity head in any flowing liquid remains constant. Thus, when the suction and discharge line sizes at the gauge attachment points are different, the resulting difference in velocity head must be in-cluded in the total head calculation.

Manometers can also be used to measure pressure. The liquid used in a manometer is normally water or mercury, but any liquid of known specific gravity can be used. Manometers are extremely accurate for determining low pressures or vacuums and no calibration is needed. They are also easily fabricated in the field to suit any particular application. Figs. 2 & 3 illustrate typical manometer set ups.

Fig. 2 Manometer Indicating Vacuum

Fig. 3 Manometer Indicating Pressure

Magnetic Drive Pumps: Recirculation Circuit

Recirculation Circuit

All magnetic drive pumps circulate some of the process fluid to lubricate and cool the bearings supporting the inner rotor.

Magnetic drive pumps with metal containment shells, also require a circulation of some process fluid through the containment shell to remove heat generated by eddy currents. For pumps with metal containment shells, the fluid recirculation path must be carefully engineered to prevent vaporization of the process liquid necessary to lubricate the bearings. A pressurized circuit as shown in Fig. 4 offers excellent reliability for pumps with metal containment shells.

Magnetic drive pumps with electrically non-conductive containment shells, such as plastic or ceramic have no heat generated by eddy currents. Since no heat is required to be removed from the containment shell, a much simpler recirculation circuit can be used.

For liquids near vaporization, a calculation must be made to ensure the process fluid does not vaporize at the bearings. This calculation includes the effects of process fluid specific heat, vapor pressure, drive losses, recirculation flow, etc. This calculation procedure can be found in the GOULDS PUMPS HANDBOOK FOR MAGNETIC DRIVE PUMPS. An external cooling system can be added to the recirculation circuit to prevent vaporization.

Fail Safe Devices

DESCRIPTION

Condition monitoring of the pump is a "key objective" and provides the user with an assurance of safety and reliability.

System and pump malfunctions can result from the following:

• No-flow condition through the pump
• Dry running as a result of plugged liquid circulation paths in the pump bearing and magnets assembly section
• Cavitation due to insufficient NPSHA
• Uncoupling of the magnetic drive due to overload
• Temperature and pressure transients in the system
• "Flashing" in the pump liquid circulation paths due to pressure and temperature transients.

These malfunctions can contribute to:

• Overheating of the drive and driven magnet assemblies
• Overload of drive motor and drive magnetic assembly
• Extreme pump bearing load conditions
• Damage to pump due to extremes in temperatures and pressures due to transients that exceed normal design.

Various fail safe devices are available with the pump to control malfunctions and provide safety and reliability including:

• thermocouple / controller
• low amp relay
• liquid leak detector
• power monitor

Magnetic Drive Pumps: Stationary Shaft

Stationary Shaft

This type of design typically uses non-metallic components such as ceramics and plastics. It is best suited for light to medium duty applications. The stationary shaft design significantly reduces the number of parts required, simplifying maintenance and reducing cost. Corrosion resistant materials such as silicon carbide ceramics and fluoropolymer plastics (Teflon, Tefzel, etc.) provide excellent range of application. The use of plastics materials does, however, limit the temperature range of these designs to 200^oF to 250^o F. (Refer to Model 3298, Section CHEM-3C).

Containment Shell Designs

The containment shell is the pressure containing barrier which is fitted between the drive and the driven magnet assembly. It must contain full working pressure of the pump, since it isolates the pumped liquid from the atmosphere. One-piece formed shells offer the best reliability, eliminating welds used for two-piece shells. Since the torque coupling magnetic force field must pass through the shell, it must be made of a non-magnetic material. Non-magnetic metals such as Hastelloy and 316SS are typical choices for the containment shell. The motion of the magnets past an electrically conductive containment shell produces eddy currents, which generate heat and must be removed by a process fluid recirculation circuit. The eddy currents also create a horsepower loss, which reduces the efficiency of the pump. Metals with low electrical conductivity have lower eddy current losses, providing superior pump efficiency. Hastelloy has a relatively low electrical conductivity and good corrosion resistance, thus is an excellent choice for metal containment shells. Electrically non-conductive materials such as plastic and ceramics are also good choices for containment shells, since the eddy current losses are totally eliminated. This results in pump efficiencies equal to conventionally sealed pumps. Plastic containment shells are generally limited to lower pressures and temperatures due to the limited strength of plastics.

Sleeve and Thrust Bearings

Magnetic drive pumps utilize process lubricated bearings to support the inner drive rotor. These bearings are subject to the corrosive nature of the liquids being pumped, thus need to be made from corrosion resistant materials. Two commonly used materials are hard carbon and silicon carbide (SIC). Pure sintered SIC is superior to reaction bonded SIC, since reaction bonded SIC has free silicon left in the matrix, resulting in lower chemical resistance and lower strength.

Hard carbon against silicon carbide offers excellent service life for many chemical applications and also offers the advantage of short term operation in marginal lubrication conditions.

Silicon carbide against silicon carbide offers excellent service life for nearly all chemical applications. Its hardness, high thermal conductivity, and strength make it an excellent bearing material. Silicon carbide must be handled carefully to prevent chipping. Silicon carbide against silicon carbide has very limited capability in marginal lubrication conditions.