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PC 101: How a PC Pump Works

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The Progressing Cavity Pump

• A progressing cavity (PC) pump, or a single screw pump, is a positive displacement pump, meaning that a fixed volume is displaced with each revolution.

• The rotor (single helix) rolls eccentrically in the stator (a double helix). When combined, pockets (or cavities) are created which moves towards the discharge end of the pump as the rotor turns.

• This web cast module session will focus on how the pump actually operates.

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Agenda

• Benefits of PC pumping principle.• Rotor and stator geometry.• Eccentric motion to create cavities.• Geometry of the seal line.• Flexible geometry to modify the pump.• Forces on drive end.• Designs to accommodate eccentric motion.• Proper bearing design.• Effects of slip.• Effect of viscosity and volumetric efficiency.• Effects of abrasion.• Effects of temperature.• Alternate design of stators - wobble versus tube.• Alternate designs of drives – bare shaft or close-coupled.• Alternative feed mechanisms – G1, G2, G3, and G4.• Limitations – run dry, compatibilities, temperature.

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Capabilities & Features

• High pressure to 2,100 PSI– L Frame = 2100 PSI (24 stage #4 element)– 2000 Series – 1200 PSI (14 stage 036)– PowerFlow metal stators = 1500 PSI– Specialty Down Hole elements (oil industry) = 2100 PSI

• Moves viscous fluids to 10 million CPS with Ultrafeed designs

• High capacity to 4,500 GPM (single stage 1500 element)• Capable of pumping highly abrasive fluids• Broadest capabilities and product offering of any positive

displacement pump technology

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Capabilities & Features

MOYNOFLOW

4500 GPM

MOYNO ABRASION Heavy

MOYNO VISCOSITY 10 million cps

MOYNO PRESSURE2100 PSI

1100GPM

250 PSILight

0.5 M cps

Other PD Pump

Competition

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Benefits of the PC Pumping Principle

• Moves abrasive fluids– Product is moved in cavities allowing particles to pass

unimpeded – Most abrasive wear is attributed to slip and speed– Limiting discharge pressure or adding stages can combat the

slip amount– Limiting speed allows the abrasive particles to pass effectively

• Non-pulsating flow– Cross-sectional area remains the same, regardless of rotor

position– No need for pulsation dampeners, check valves, etc.

• Low Net Positive Suction Head (NPSH) requirement– Capacity stays constant even under varied suction conditions

• Wide range of viscosity from water-like to super viscous

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Benefits of the PC Pumping Principle

• Discharge pressure independent of speed– Pressure is predictable knowing the flow and viscosity of the pumped

fluid– Pump overcomes pressure vs. discharge line losses

• Flow directly proportional to speed– Because the pump is positive displacement, an increase in speed

creates a proportional increase in flow• No valves

– The cavities within the pump are sealed, stopping a leak path from occurring

– Residual pressure would have to overcome starting torque in order to turn the pump rotor

• Quiet Operation– Typically the loudest component of the pump system is the motor fan

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Benefits of the PC Pumping Principle

• Reversible– Pumps are fully reversible for ease of installation (check seal

springs)– Flow is unaffected by reverse rotation– Pressure can be limited during reverse flow based on U-joint

pressure capability• Low shear pumping action

– Product moves gently through the pump via a cavity – Product shear is confined to the sealing line

• Passes solids to 2.8 inches– Because of the product movement in the cavities, large particles

can be passed without damage to the product or pump– Information is available as to maximum solid size per pump

model

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Benefits of the PC Pumping Principle

• Will not vapor lock– Pumps are capable of moving air, fluid, or combination of both

without issues.– Caution must be used as PUMPS CANNOT BE RUN DRY!

• Suction lifts to 28 feet– The cavities in the pump are sealed allowing the pump to pull

very high lifts– Viscosity, solids, and pump sealing can limit suction lift capability

• Pumps corrosives and chemicals – full pH range– A variety of standard metals and elastomers are available– Exotic materials and coatings can also be employed for very

harsh environments– A variety of sealing systems can be used depending on fluid

requirements

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Benefits of the PC Pumping Principle

• Fluid temperatures to 500°F– Metal rotor and stator combinations can be used for extreme

temperatures– Elastomer combinations with maximum temperature ratings to 350°F

• Self-priming– With product in the suction line the pump will self-prime– Pump is capable of pumping air until product fills the cavities– For high viscosity or solid laden liquids a water line in the suction may

be required to prevent run dry• High solids concentration

– Fluids with over 50% municipally and 90% industrially are possible– Special pump types are used to “stuff” product into the pump elements

• Flow only slightly affected by pressure– Pumps exhibit low slip amounts (loss of flow) until the pressure gets

close to the pressure capability of the rotor/stator combination

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Geometry

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Rotor Geometry

• Circular cross-section

• Machine in helical shape

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Stator Geometry

• Oval cross-section

• Similar helix, but twice the pitch length

• Elastomer, metal or Teflon®

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Cavities

• Rotor turns eccentrically side to side in stator

• Creating cavities and progressing them

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Progressing Cavity

• Helical seal line isolates discharge pressure from the suction side

Packing/Mechanical Seal On Suction Side:Does not see the abuse of the discharge pressure

Suction

Discharge

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Cavity Opening

Progressing Cavity• Large cavity inlet

opening, up to 5.6” on K800

• As rotor moves down and one cavity diminishes, another cavity is opened at 180° (Top).

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Minor Diameter

Cavity Rating for Particles

Rule of Thumb: For excellent particle definition,...

• Moyno rates the pump for ½ the minor diameter of the cavity (peak-to-valley dimension of rotor)

• Particle rating of K800 = 2.8”

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Cavity Shape

• Viscous Sludge Cake Directly out of Pump- Retains approximate shape of cavity

Note: Fill efficiency of HS System

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Geometry of the Seal Lines

• Rotor has compressive fit with stator

• Helical seal line allows for an “Augered Style” flow pattern

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Importance of Seal Line Geometry

• Compressive fit controls slip for highly metered flow capability over wide viscosity range.

• Helical seal line allows for pulse-less, low shear pumping action with minimal velocity

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Flexible Geometry Offers

• PC pump is based on an axial geometry which allows:– Ability to add stages to the pump by extending the length– Ability to oversize (abrasion) or undersize (temp swell) the rotor

to control the compression fit– Ability to provide bigger drive ends for higher torques

• Thereby matching the pump to the application.

3 STAGE (3L)

1 STAGE (L)

Axial Geometry

1 Stage

3 Stage

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Benefits of Flexible Geometry

• Minimizes slip – reduces RPM• Increases pressure capabilities • Extends pump life on abrasives• Improves metering capabilities• Increases temperature capability of stator

0 100 200 300

CA

PAC

ITY

- G

PM

50

100

DIFFERENTIAL PRESSURE - PSI

3 STAGE (3L)

1 STAGE (L)

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• Drive end designs to accommodate the eccentric motion

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PC Drive

• The PC drive end must convert the following: – Concentric rotary motion of the gearmotor– To an eccentric (side to side) and rotary motion of the rotor – While handling the high reactionary forces:

• Thrust force (Exerted by Differential Pressure) • Rotational forces (Hydraulic Torque + Stator Drag) • Overhung loads due to Eccentric motion.

0 PSI100 PSI

Thrust

Rotational

GearMotor

ECC

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Eccentric Motion

Handling the eccentric motion is broken into 3 technology components:

Universal Joint

Bearings Design

Drive Shaft

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Universal Joint Types

• Heavy Duty – 2000 gear join

• General Purpose – pin joint– 1000 – covered pin– L-Frame – partially

covered– Sanitary – open

• Flexi-shaft – optional• Cartridge – 500 series

Connecting Rod Drive Shaft

Pin Retainer

PinJoint Seal

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• Lower leverage of Ecc force on bearings.

• Less shaft deflection

Drive Shaft Types

Length

Fecc

Bearings located between the joints

L

Fecc

Hollow Shaft

Standard Shaft

Both joints in the suction housing

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Proper Bearings Design – 2000 & L-Frame

• Split bearing spacers provide the proper dimension between the heavy duty taper roller bearings.

• Bearing lock nut pulls the assembly together and locks it into position. No shimming is required for easy maintenance.

• Stack–up dimensions precisely set by solid metal shoulders machined into the bearing parts.

• Bearing assembly tightens the radial bearing onto its race with increased thrust load.

Hollow Shaft

Cover Plate

Spacer

Bearings Lock Nut – Threads onto shaft

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Moyno 1000, Seepex and Netzsch Bearing Design

• Low cost snap rings used to set bearings. – Loose tolerance is required in snap ring holes for ring to be

installed.– Snap rings will bend as thrust load is increased. – Front radial bearing will pull back from race and create shaft

deflection

Thrust

Thrust

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• Effects of Slip, Viscosity, Abrasion and Temperature

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What is Slip

• Back flow in the pump (internal leakage) as pressure is generated

• Dead head pressure = 100% slip

0 PSI160 PSI

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Effects of slip

• Loss of flow – need to overcome slip before getting flow• High velocity slip-back causes wear with abrasives fluids

•Back flow through the pump

0 PSI160 PSI

• Internal pump velocity = 1 to 5 ft/sec

• Slip velocity = 13 to 20 ft/sec

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Slip

Based On• Press Differential• # Stages• Viscosity

• Slip is independent of RPM: same slip amount at 50 RPM as 500 RPM

Press/stage

12

10

8

6

4

2

0

20 40 60 80 100 120 140 160 180 200 Differential Pressure

(PSI)

Pressure and SlipCapacity (GPM)

Slip @ 120 PSI

Slip @ 60 PSI

Viscosity and Slip

20 40 60 80 100120140160 180200

12

10

8

6

4

2

0

Differential Pressure (PSI)

Capacity (GPM)

High Viscosity

Low Viscosity

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Effects of Viscosity

• The more viscous a fluid, the slower the pump will have to run in order to permit the fluid to flow into the cavity.

• Even at reduced speeds, the pump may not develop 100% volumetric efficiency and this must be accounted for in the selection process.

Cavity only half full

•1 CPS = Above 1800 RPM

•100 CPS = 700 RPM

•1000 CPS = 150 RPM•10,000 CPS = 30 RPM

Loss of Fill Efficiency starts at

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Effects of Viscosity

• Most fluids shear thin to a level well below their static viscosity

• Pumps are applied based on shear viscosity in a flow condition. Moyno can provide shear rate testing free of charge

• For higher viscosity ranges, open throat style pumps are used with auger screw on the connecting rod

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PEC 449 Developed to Determine Volumetric Efficiency

• CAPS utilizes a math model of PEC 449 curve

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Effects of Viscosity

Rule of Thumb• Minimum Recommended Volumetric Fill

Efficiencies Application Efficiency• Transfer 50%• Metering 70%• Extrusion 95-100%

• CAPS uses the term “Intake Index”, where 0 = 0% and 10.0 = 100%

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Effects of Slip & Viscosity on RPM

( GPM + Slip ) 100 RPMVol Efficiency Theo Capacity

xRPM =

Slip is based on:

• Press / Stage

• Element Size

Vol effic is based on• Pump Speed• Viscosity• Absolute Pressure

Desired

Flowrate

Element Size

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Effects of Slip & Viscosity on Brake HP

HP = ( HP ) x ( Multi ) Rot/sta 0 PSI Temp

( GPM + Slip) PSIVol Effic 1714

Hydraulic

HP = x

HP = HP + HP + HP + HP Total Rot/sta Hydraulic Drive End Visc or Solids

HP = Taken From Performance CurveDrive End

HP = ( Visc Multi ) x ( RPM ) x ( # Stages)Visc 100 RPM

Compressive fit of rotor/stator

Work of the pump

Bearing and stuffing box friction

Drag of fluid viscosity/solids

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Effects of Abrasion

Abrasive fluids = Wear • Wear is proportional to speed; minimize speed to minimize wear.• De-rate pressure per stage to limit slip amount ... 87 PSI for no

abrasion; 20 PSI for heavy abrasion.• Oversize rotor to maintain compressive fit longer.• Use abrasion resistant stator material or softer durometer

elastomers.

Abrasive Characteristic Fluids

None Water, Polymer, Oil

Light Sewage, Milk or Lime

MediumSludge, Clay or Gypsum Slurries, Chocolate, Drilling Mud

HeavyEmery Dust, Lapping Compounds, Grout, Sand, Granulated Sugar

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Effects of Temperature

• Stator– Some stators will start to swell with temperatures above 130°F,

and start to shrink below 40°F.– With the swelling or shrinking the compressive fit on the

rotor/stator combination is changed, thus requiring the rotor to be specially sized to compensate for this ( >160º = undersize rotor).

– Under extreme heat or cold, elastomer stators may not be appropriate; designs with no elastomers are available.

• Rotor and Drive Train– Metal parts such as the rotor and drive train tend to expand and

contract at a much lower rate than elastomer counterparts.– Metal rotor and stator combination can be used for extreme

temperature because they swell or shrink at the similar rates.

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• Alternate Designs of:– Stators– Drives– Feed Mechanisms

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Alternate Stator Designs

• Tube Style – Standard Elastomer– Standard Elastomer Stators

• 2000 Metering• 1000 Sanitary• L-Frame 600 Series

– PowerFlow Metail Stators

• Eccentric motion allowed for by two universal joints on the drive train

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Alternate Stator Designs

• Wobble Stator– 200 series– 300 series– 400 series

• Eccentric motion allowed for by: – One joint on the drive train– “Skirt” shape of stator

Stator

Suction Port

Rotor

Flexible Joint

Discharge Port

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Moyno UltraFeed Technology

G1

G2

G3

2000HS

G4

Bridge Breaker

Alternate Feed

Designs

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Alternate Drive Designs – Close Coupled or Bare Shaft

• Close coupled offers the lowest cost configuration

• Drive is overhung on motors less than 40 hp• The majority of the competition uses CC• CC utilizes the gearbox bearings for thrust and

radial loads• Bare shaft pumps have bearings internal to the

pump• Requires use of a coupling and guard• Allows the use of belts and sheaves• Considered the most robust design

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Pump Limitations

• Pumps cannot be run dry– Catastrophic stator and rotor damage can occur– Stator run dry device or loss of flow sensor available

• Material compatibilities must be verified– Swelling, hardening, pitting, or total failure can occur– In-house compatibility testing available

• Pumping temperature must be verified– Swelling or degradation can occur– Elastomer ratings to as high as 350°F, metals to

500°F– Oversize rotor for low temperature may be required– Undersize rotor for high temperature may be required