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The DV-1 Vertical Drivehead does not have an ‘Emergency Stop’ handle to stop the movement dur-ing normal operation. Refer to the documentation of the electric control panel to stop the electric
motor in case of an emergency.
Emergency Shut Down During Recoil/Backspin
The DV-1 Vertical Drivehead has a handle to control the hydraulic fluid flow that allows to stop the
backspin in a recoil scenario. To stop the drive completely close the valve (refer to Fig. 1.4 to iden-
tify valve handle location).
Use this ‘Emergency Shut Down’ handle immediately in case of a dangerous situation ...
• … for life and limb or
• … material damage of the unit or attached tooling.
WARNING
When the hydraulic brake valve is closed during recoil energy will be re-tained in the rod string. This energy MUST be released before any other jobis performed on the drive.
b) Ensure that the slot on the bottom of the clamp is correctly fitted with the main shaft and tighten the
nuts manually to maintain the two polished rod clamp pieces perfectly aligned. Is very important to
maintain this alignment in order to avoid angular forces in nuts and bolt heads.
c) Using an adequate tooling, tighten the nuts following the sequence indicated below, this tighten must
be progressive for each bolt until 340 Nm (250 lbs.ft) torque is reached.
1) Evenly tighten bolts 1, 2 and 3. (Do not tighten bolt 1 all the way, before moving to
bolt 2 and do not tighten bolt 2 all the way, before moving to bolt 3).
2) Evenly tighten bolts 4, 5 and 6. (Do not tighten bolt 4 all the way, before moving to
bolt 5 and do not tighten bolt 5 all the way, before moving to bolt 6).
CAUTION
When doing the tightening, always follow the same sequence and maintainthe two polished rod clamp pieces alignment to ensure correct polished rodclamp fitting.
12.Lower the stuffing box assembly onto the flow tee and bolt or thread it into place. Tighten all wellhead
fittings to the maximum torque specifications.
13.Remove the pony rod and connect a sucker rod coupling.
14.Make sure all connections and screws are tightened as well as make sure of the drivehead belt ten-
sion.
CAUTION
Be sure connections are completely tight before starting up the unit. Failureto tighten connections correctly will damage drivehead equipment andcause loss of performance.
15.Check for friction between moving parts in order to avoid any moving parts malfunction.
Sheave-Belt guard must be always positioned and locked before start-up.Never put your hands on the moving parts of the drivehead in operation.
16.Before turning the mover on remove the plug that is on the top of the drivehead and put the oil relief in
its place.
CAUTION
This oil plug must be replaced by an oil relief before start-up to avoid inter-nal oil pressure. Not doing this could last on damaging drivehead oil retain-ers.
17.Refer to chapter 4 for drivehead starting up procedures.
CAUTION
DV1 drivehead is design for vertical well application with a maximum devia-tion (from the vertical) of 3 degrees.
Maximum ratings are individual specs. Maximum torque, HP and speed can-not occur simultaneously.
• The maximum torque is limited by the braking system.
• Ca90 load is for 90000 revolutions. Reducing load by one half increases life ten times. Reducing the
RPM by one half doubles the hours of life.
• Various connection types are available on request.
• Maximum sheave diameter depends on motor size. Smaller motors can accommodate larger drive
sheaves.
Drive Type Drive Ratio Drive Style
Input Shaft Main Shaft Type
Maximum Input Polish Rod Torque - (1) 750 ft x lbs 1017 N x m 30200 lbs 13696 kgf 116500 lbs 52834 kgf
Maximum Polished Rod Speed Maximum Motor Size - Single Motor 25 hp 18,5 kw Polished Rod Size 1.1/4 in 31,75 mm Maximum Suggested Temperature (Comp.-Temp.) Seal - 230 °F Seal - 100 °C Box oil type
Oil quantity
Height 47 in 1194 mm Drive/Frame Weight 930 lbs 422 kgf
1017 N x m
Brake oil type Oil quantity
API Wellhead Connection - (3)
Prime Mover
Driven Sheave Maximum Diameter 23,60 in 600 mm Driver Sheave Maximum Diameter - (4) 9,00 in 230 mm Driver Sheave Minimum Diameter - (5) 4,50 in 115 mm Drive Belt type Max. Number of Belts Minimum Center Distance 22,7 in 576 mm
Dimensions & Weights (excluding motor)
- ISO Rating
DRIVE NAME / MODEL DV1
Vertical Drive -
Well equipment compatibility
Automatic external hydraulicbrake/manifold with needle valve
200 IEC or 326T NEMA
Bearing Box Vertical
Hollow Shaft Ratings
600 rpm
Mobil SHC 629
8,7 L
17 L
Backspin resistance torque Maximum backspin Pump speed - up to
1 Support ArmSupport arm coupled to the drivehead’s structure in order to as-sure greater structural stability (Eliminating excessive vibrations)
2 SheavesSheaves used to reduce system rotation to the rotating speed de-sired.
3 BeltsBelts used to connect the motor sheave with the driveheadsheave.
4 Electric MotorElectric Motors connected to the drivehead trough the sheavesand belts, to give movement to the system.
5 Ejection ClampClamp connected to the polished rod in between the stuffing boxand the housing in order to avoid the ejection of the polished rodin case of a backspin.
Operation of the DV-1 Vertical Drivehead consists on …
• …starting Up Procedure.
• …shutting Down Procedure.
• …braking System Operation Procedure.
4.1 STARTING UP PROCEDURE
WARNING
Wear all protective clothing recommended when working in close proximityto the drivehead.
1. Approach to the well head with caution, observing the other wells operating nearby. It is advisable to
set up a protecting barrier between the well and personnel before the start up.
CAUTION
If by any chance the operating conditions are unsafe, call your supervisor.
2. Make sure the clamp is properly installed, the belt guard in place and the stuffing box hand tight.
3. If you are performing this operation alone, make sure that someone else knows what you will be doing,
exact location and schedule. Minimize the quantity of people around the well. It is advisable to set up a
protecting barrier between the well and personnel before the start-up.
WARNING
The drivehead start up must be done only by trained and experienced per-sonnel who understand the normal and abnormal situations concerning“backspin” rotation and all the risks involved. The indications and recom-mendations included in this manual can NOT substitute a proper trainingprogram for operators.
4. Inform everybody present at the local about the risks involved. (i.e. “tailgate” or safety meeting).
WARNING
Do not allow more than 30 cm of polished rod above the drivehead. Therecan not be any pony rods connected to the top of the polished rod even ifthey are inside this range.
5. Set all casing, tubing, flow line and drivehead components correctly for operation.
CAUTION
Be sure connections are completely tight before starting up the unit. Failureto tighten connections correctly will damage drivehead equipment andcause loss of performance.
WARNING
Sheave-Belt guard must be always positioned and locked before start-up.Never put your hands on the moving parts of the drivehead in operation.
6. For wells fitted with VFD (Variable Frequency Drive):
a) Turn ON/OFF switch to “OFF” position, then turn ON the main circuit breaker.
b) Verify that all the shutdown parameters are set.
c) Set VFD to zero frequency or minimum speed.
d) Set for normal operating mode with external shutdown enable.
e) Set the panel to show current (amperage) and torque, ensuring that all safety shutdown proc-
esses are properly set.
f) Put the ON/OFF switch on position “ON”.
7. During the initial operation (e.g. first few minutes), monitor for any unusual noises, vibrations, leaks and ex-
cessive temperatures or pressures. If anything abnormal is detected turn the equipment off and call your
supervisor for assistance.
WARNING
Turning on and off the equipment in excess can cause overheating of thebreaking system and drivehead oil.
8. Check and adjust the overpressure controller of the production line to the desired value.
9. Monitor all pressures and check for leaks.
CAUTION
Make sure connections are completely tight.The operator must be familiar with all applicable environmental regulationsin the event of leakage or spillage and prepared to take appropriate steps forcontrol and removal.
10.Check if the stuffing box is operating properly without excessive leakage.
CAUTION
ALWAYS switch off the drivehead BEFORE connecting or disconnecting anydrivehead components! NEVER attempt to do so with the drivehead moving.
To do so may cause injury to personnel and will damage the equipment.
11.Inform your supervisor that the start up is done and that you are leaving the area.
Wear all protective clothing recommended when working in close proximityto the drivehead.
1. Become familiar with well operating conditions prior to shut-down including speeds, production, current
(amperage) and recent interventions.
2. Approach the well with caution to perform a visual inspection.
3. If you are performing this operation alone, make sure that someone else knows what you will be doing,
exact location and schedule. Minimize the quantity of people around the well. It is advisable to set up a
protecting barrier between the well and personnel before the shut down.4. Inform everybody present at the local about the risks involved. (i.e. “tailgate” or safety meeting).
WARNING
The drivehead shut down must be done only by trained and experiencedpersonnel who understand the normal and abnormal situations concerning“backspin” rotation and all the risks involved. The indications and recom-mendations included in this manual can NOT substitute a proper trainingprogram for operators.
5. Check for unusual noises.
CAUTION
If for any reason at any point of the procedure you suspect the operation isunsafe, keep yourself and all the personnel behind a barrier and call yoursupervisor immediately.
6. If the necessary steps have not been taken to control backspin, a protection barrier should be provided
near the control panel during the proceedings and make sure everyone is away from the well prox-
imities before initiating the shut down operation.
WARNING
Never operate a drivehead with a malfunctioning breaking system. A highspeed backspin may damage the equipment and put personnel at risk.
7. Check the following:
a) Well head pressures.
b) Motor current (if the current is above the usual the backspin speed will be higher)
c) The oil level of the braking system and drivehead.
8. If the well is fitted with VFD, use it to gradually slow the speed to the minimum possible before shutting
it down totally.
9. Turn off the drivehead through the main panel and observe the braking system performance.
10.Remain behind protection; observe any abnormal backspin (e.g. excessive speed).
Do not approach to the wellhead until the backspin stops.
Turn off and lock the circuit breaker on the main panel before doing any in-tervention.
11.For breaking systems with adjustable holes, open the valve completely to make sure the rods column reach
balance.
CAUTION
Even after the drivehead shutdown and the stopping of the backspin, thereis still a possibility of recoil. This extra recoil is caused by the equalizationbetween the fluid inside the production tubing and the fluid inside the cas-ing.
4.3 BRAKING SYSTEM OPERATION PROCEDURE
Since the characteristics of the wells where the driveheads could be installed are unknown, braking systems
are always set for maximum operating conditions as a default manufacturing safety procedure.
1. The braking system is designed to operate at the maximum allowed nominal torque in a safety speed and
temperature range.
2. The brake system of the DV-1 Vertical Drivehead operates automatically if the valve “A” is left opened (fac-
tory default condition). If for any reason it is desirable to block the reverse movement the valve “A” should
be completely closed before starting the shut down procedure. The lock nut “B” is used to maintain the valve
“A” in the desired position.
3. There is a direct relation between the torque accumulated in the rod string and the pressure indicated in the
manometer. For the maximum nominal torque, the pressure will reach ~160 Bar.
NOTICE
In order to protect the hydraulic motor any pressure above 247 bar willcause a relief valve to open.
Weatherford has recently decided to be more involved in the applications of PCP driveheads for many motives.
History shows that most of the serious incidents with any PC Pump driveheads have occurred when the pump
is seized downhole and the PC Pumping system has been torqued up in an attempt to free the pump. In a di-
rect electric application, this input torque is typically limited only by the maximum horsepower the motor can de-
liver and the rod string’s ability to transmit torque down to the pump. Unknown for most operators is the fact
that all electric motors have the ability to deliver over 250% of the full load nameplate horsepower. This poten-
tial applied torque can far exceed the published structural and backspin control limits of the drivehead.
One way to limit the maximum torque input is to restrict the motor size and sheave ratio in order to limit the
maximum torque that can potentially be applied. Graphs have been prepared to illustrate safe operating limits,
and define where there is a potential problem with applying excessive torque to the system. By using the relevant DV-1 Vertical Drivehead graph and comparing the sheave ratio versus connected horse-
power for any given application the operation of the PC pump system will be as follows: • In Zone 1: The PC Pumping System is inherently safe. It is not possible to apply more torque than the
recommended maximum input torque with the equipment specified.
• In Zone 2: Operation should be carefully considered. If the motor was operated at its extreme torque limit
(potentially 250% of nameplate rated horsepower) such as to free a stuck pump during startup, it may be
possible to exceed the recommended load rating of the drivehead.
• In Zone 3: Operation is potentially dangerous unless an acceptable torque-limiting device is used (e.g.
VFD). Without such a device, it is likely that the load rating of the system can be exceeded.
If a sheave/horsepower combination falls within the Zone 2 or 3 of the curve, it does not mean that the
combination cannot be used. What is being illustrated here is that under certain circumstances (e.g.
seized pump), there is a potential risk for a recoil (back spin) event where the torque stored in the rod
string may be larger than the maximum drivehead rated torque.
Note that the level of potential risk will be affected by the sheave ratio, the maximum torque the motor can
deliver and the ability of the drivehead backspin control device to safely handle the torque and the energy
stored in the system. The backspin control system will experiment a peak torque at the beginning of this
operation; if this torque surpasses the rated capacity of the drivehead it may cause the mechanical failure
of one of its components during the first seconds. However, note that even if the peak torque is not exces-
sive, if the total energy stored in the system (which is affected by the completion geometry and the welloperating conditions) is too high and the backspin occurs too fast, it could lead to an overheating and
eventual failure of the backspin control system.
When operating any PC Pumping system in the Zone 2 or 3 it is recommended to use some type of accu-
rate torque limiting device. This torque control can be a vector flux drive controller with the torque limits set
below the drivehead rated capacity. It is important to remember that not all VFD's have vector technology;
for instance, a scalar drive will not provide accurate torque control. Torque limits on the vector drive must
not be increase to free a stuck (seized) pump. Doing so may damage the equipment and put personnel at
Once the proper drive has been selected and installed, they need to be maintained. It is imperative that the
manufacturer's maintenance procedures be followed, including routine oil changes and checks of the
backspin control device performance.
WARNING
Note that the input torque is typically limited by the maximum horsepower the
motor can deliver and the rod strings ability to transmit torque down the pump.
However, electric motors have the ability to deliver over 250% of the full load
nameplate horsepower and over 250% of the maximum published torque. In a
seized pump scenario and in the absence of torque limiting device, the system
will torque up in an attempt to free the pump. This applied torque can far ex-
ceed the published structural and backspin control limits of the drivehead.
4.5 DRIVEHEAD REMOVAL PROCEDURE
WARNING
Wear all protective clothing recommended when working in close proximity
to the drivehead.
1. Switch off the drivehead as described on the shutting down procedure on this Chapter.
WARNING
The drivehead removal must be done only by trained and experienced per-sonnel.
The indications and recommendations included in this manual can NOTsubstitute a proper training program for operators.
2. Disconnect all the hoses or wiring to the electric motor.
3. Attach a 600mm pony rod and rod coupling to the polished rod.
4. With the use of a flushby unit or rig attach the working line to the 600mm pony rod.
CAUTION
All lifting gear must have a minimum lifting capacity of 3.000 kg / 6.615 lb.
Ensure that all lifting equipment is in proper working condition.
5. Pull up the polished rod to pick up the rod weight.
6. Begin to loosen off the polished rod drive clamp bolts.
7. Once the clamp has been loosened off, begin to pull up the polished rod (approx. 600–900 mm).8. Isolate the production tubing through the BOP installed below the drivehead and close the flowline valve to
Only WEATHERFORD trained personnel may carry out troubleshooting, ser-vice and maintenance tasks.
Other personnel may be unaware of required methods and expertise, possi-bly leading to dangerous situations.
CAUT ION
Cleaning and maintenance intervals are crucial for the operational safety ofthe unit and must therefore be strictly adhered to.
Disregarding this caution will cause a potentially hazardous situation, whichcan result in personal injury and/or material damage.
CAUT ION
Use only original WEATHERFORD spare parts. Part numbers can be found inthe parts list in Chapter 7 of this manual.
Only persons having specific knowledge and experience in Drivehead sys-tems may carry out work on hydraulic equipment.
CAUT ION
Surfaces may be hot.
Let equipment cool down or wear suitable personal protective equipment.Clean or service only with drivehead stationary and cold!
5.1 PREVENTIVE MAINTENANCE SCHEDULE
DESCRIPTION FREQUENCY SECTION
Stuffing Box
Grease the packing Daily during the first two days of operation. After ini-tial period at least once a week but might be morefrequent depending on application details
5.2
Change packing Yearly or before if excessive leakage occurs 5.3
Bearing Box
Oil Change First change after one month, then repeat annually 5.4
Belts
Belts inspection Every three months, change if worn out 5.5
Braking System Gears
Oil Change Yearly 5.6
Hydraulic break system
Oil Change Yearly 5.7
Overhaul maintenance(bearings, ratchet system)
Should be performed only by Weatherford or trained personnel.Refer to specific training material for instructions.
1. Shut-down the drivehead following the shutting down procedures on Chapter 4, Section 4.2.
2. Close flow line valve to production tank.
3. Set a safety clamp above the stuffing box to secure the polished rod during maintenance (see Fig. 5.3
for an example of safety clamp installed).
4. Open the hinged belt guard.
5. Loosen the two motor plate tension screws.
6. Remove the old belt(s).
7. Install new drive belt(s) and tighten to the appropriate tension checking belt deflection to be equal to1.6% of sheaves’ centers distance (see Fig 5.4 for a schematic of how to measure this deflection).
1. Certify clamp jaws are in perfect conditions.2. Place polished rod clamp support between drivehead and wellhead flange.
3. If necessary replace stuffing box flange studs for longer ones.
4. Tighten lock bolts following this sequence:
1 3
4 2
CAUT ION
More than one polished rod clamp could be used for applications with largeaxial load. Weatherford Application Engineering must be consulted to de-termine number of clamps required.
Engaging
1. Switch off the drivehead by following the shutting down procedures on Chapter 4, Section 4.2.
2. Tighten screws using the spiral threads as a reference.
3. Torque up all screws with 339 N.m following sequence shown in step 4 of installation procedure.
4. Double-check bolts torque of 339 N.m.
CAUT ION
Screws must be tighten and loosen slowly to avoid any screws o´rings damage.
Disengaging
1. Certify rods load is being supported by upper drivehead clamp.
2. Slowly loosen screws staying alert for any eventual additional energy release.
3. Totally loosen all four screws.
4. Turn on the drivehead by following the starting up procedures on Chapter 4, Section 4.1.
WARNING
• Maximum axial load per clamp must not exceed 4 Tons (metric).• Polished rod clamp must never be used as a rod torque safety device.
• Polished rod clamp must be used only for rods axial load supporting.
Symptom / Possible Cause Possible Cause Corrective Action
Stuffing box with excessive leak-age
Stuffing box cap is too loose Tighten the Stuffing box cap to minimize leakage.
Stuffing box cap showing exces-sive wear
Possibly due to excessivetightening
Replace the Stuffing Box Caps.
Bushings excessive wear Possible misalignment (dueto excessive unsupportedweight)
An indication of misalignment is that the cap willnot thread on and off easily. Adjust the position ofthe drive with support arms to minimize load (mo-mentum) of the motor assembly on the driveheadbase.
Polished rod seized inside stuff-ing box
Possibly due to wrench marks File off any wrench marks.
6.2 HYDRAULIC BRAKING SYSTEM
Symptom / Possible Cause Possible Cause Corrective Action
Inconsistent Pressure reading Pressure indicators are faulty Check pressure gauges
Excessive noise and/or noise
during backspin
The oil dispenser could be
running out of hydraulic oil
Check hydraulic oil level and fill up if necessary,
refer to Chapter 5.’Oil Change Procedure. Checkfor oil leakages. Check hoses and connectors forproper engagement
Excessive backspin speed Damage in the Pressure Re-lief Valve or lack of choke inthe manifold
Replacement of whole manifold; send old manifoldfor inspection and/or refurbishment
All Weatherford PC Pump driveheads have moving external parts like drivehead sheaves, electric
mover sheaves, transmission belts, main shaft, polished rod, and polished rod clamp.
The driveheads are built with a belt guard and a clamp guard, and there is also the possibility of a
greaser guard to ending the possibility of any contact with the polished rod when equipment is operat-
ing.
WARNING
• Never put your hands on the moving parts of the drivehead in operation.
• Always maintain the polished rod clean for later RPM reference, cap tightening, etc. If clean-ing of the polished rod is necessary, do so with the drivehead stopped.
• The Sheave/Belt guard and the clamp must always be positioned and locked before start-up.
• Always stop the drivehead for any operation that involves contact with moving parts.
• Watch out for clothes, gloves, cloths, ropes and other materials that may get caught and putpersonnel at serious risk.
• Before stopping the drivehead always make sure that the brake is set-up to lock the drive-head avoiding an accelerated backspin.
• Before turning on the drivehead always check for friction between moving parts in order toavoid any moving parts malfunction
Symptom / Possible Cause Possible Cause Corrective Action
Cannot get a consistent read-ing of RPM at the Polished Rod
Missing or dirty reflect-ing element on the Pol-ished Rod
Turn the equipment off and then replace reflecting tape.Never try to clean the polished rod while the drive-head is rotating.
Fractured or broken Sheave Excessive vibration, ex-cessive backspin speed
Inspect brake, perform a controlled backspin operationand monitor speed (see chapter 4 for safety remarks).Replace Shaves. Never forget to close and lock thesheave guard and most importantly, never operate adrivehead with a malfunctioning breaking system.
Excessive belt wear and/or fail-ure
Belt breaking happensfor many reasons, such
as: over tightening, mis-alignment, and sheavechannels problems.
Make sure the belts are always correctly set-up, watch outfor wear and tear, replace them in the end of their opera-
tional lifetime, and most important, always close and lockthe sheave/belt guard.
Bent Polished Rod Mechanical damageduring installation; ex-cessive length; exces-sive backspin speed
Check Polish rod length; Replace the Polished Rod andrelocate the Polished Rod Clamp. This problem occurswhen too much rod length is left above the polished rodclamp. In case of a high speed backspin rod bendingor even rod breaking may occur with a extreme riskfor field personnel.
Applied torque is that applied to the top of the rod string by the surface drive.
Auxiliary Equipment
Auxiliary equipment is any component which can be changed by the end user. Examples are sheaves, belts,
motors guards, motor controllers, torque limiting devices, and speed limiting devices.
Backspin
Backspin is the process by which the surface drive turns in the direction opposite to normal operation. Back-
spin is driven by the energy stored in the rod string (strain energy) and in the residual differential fluid pres-
sure across the pump after the system is shut down.
Dissipation Rate
Dissipation rate refers to the power transferred to the surroundings by the braking system in the form of heat.
Dynamic Fluid Level
Dynamic fluid level is the distance from the wellhead to the top of the liquid column in the annular space be-
tween the tubing and casing during normal operation.
Electric Motor Brake
Electric motor brakes control the power from the electric prime mover during backspin to create a braking ef-
fect on the system.
Energy Capacity
The energy capacity of a surface drive is a measure of the total work the brake can do over the expected du-
ration of a shutdown event. For example, a braking system which manages stored energy by absorption and
not dissipation has a finite energy capacity defined by thermodynamic characteristics and maximum allowable
operating temperature. A brake which can dissipate energy as fast as it is generated by the shutdown process
has an infinite energy capacity.
Flow Losses
Flow losses refer to internal friction of moving fluids resulting in pressure loss.
Fluid Dump Case
The fluid dump case describes most normal shutdowns where power to the surface drive is removed thereby
allowing backspin. The differential fluid pressure across the pump causes the rotor and rod string to rotate in
the direction opposite to normal pumping, allowing fluid to flow from the production tubing back through thepump. Backspin continues until torque resulting from differential pressure across the pump equals friction
Strain energy is the energy stored in the elastic torsional deformation of the rod string. Strain energy is typi-cally of smaller magnitude than the fluid energy, but may be released much more quickly thereby placing dif-
ferent requirements on the braking system.
Stuck (Seized) Pump Case
The stuck or seized pump case describes one extreme of the possible conditions at shutdown. PCP rotors
sometimes become "stuck" in the stator and become effectively locked together. The top of the rod string
continues to turn while the bottom stops, causing the rod string to further wind up as a torsional spring caus-
ing increased torque. When drive torque is removed, backspin may occurs with a extremely high acceleration
for a very short period, potentially leading to a very high backspin speed.
Thrust Bearing
Device typically contained in the surface drive which reacts axial load from the rod string while allowing it to
rotate.
Torque Limiting Device
A torque limiting device prevents the system from applying torsion greater than a prescribed value to the rod
string. Slow reaction time and dependence on ambient temperature makes "heaters" in the electric power
supply system unacceptable as torque limiting devices. Acceptable devices will apply torque no greater than
110% of the torque limiter set point during a stuck pump event.
Tubing Head Pressure/Casing Head Pressure
Tubing head pressure/casing head pressures are measured at the wellhead and contribute to the total differ-
Weatherford currently manufactures different kinds of wellhead drives to match diverse application en-
countered by progressing cavity pumping systems. Each one has been designed for a special purpose, to
choose the best drivehead for a specific application the following should be considered:
• Depth of well
• Fluid level
• Pump size
• Size of sucker rods, polished rod and tubing connection
• Operating torque
• Desired speed range
• Prime mover (electric motor or internal combustion engine)
When purchasing a PC pumping unit, the design considerations play an important role in the safe opera-
tions of the unit. The application designer must establish the maximum surface loading and ensure the
equipment being purchased will operate within its rated limits. The loading or work done by a PC pumping
system is primarily determined by the following:
• Pump intake pressure
• Pump discharge pressure
• Rod string/tubing friction
• Internal pump friction
Several other factors influence these parameters and they usually change throughout the life of an oil well.
Other factors may include:
• Fluid contaminants
• Pressure, volume, temperature properties of the production medium, reservoir characteristics, tub-
ing roughness
• Side wall stress as a result of tubing/rod contact
• Tubing and casing pressure fluctuations• Interference pump fit between rotor/stator
Computer aided software tools are available to help determine these factors. Calculations must be made
before purchasing a unit. When predicting load limits, a safety factor of at least 10 percent should be con-
sidered to account for error associated with the reliability of assumptions or the accuracy of mathematical
correlations.
Operating loads may change through the operating cycle life. After the initial start up, actual operatingloads should be confirmed to verify design expectations. If the system loading exceeds the design,
changes to operating parameters or equipment are necessary.