pump selection for laboratory scale fluid handling selection for laboratory scale fluid handling by...

Pump Selection for

Laboratory Scale Fluid

Handling

by Bruce Smith, Applications Engineering Manager

As laboratory processes grow in scale and economics drives towards

automation, how to automatically move the fluids becomes a design

issue with an ever-increasing number of potential answers. The

immense variety of pump types available can be overwhelming.

Key Challenges:

• Sorting through the vast offerings of

pumps on the market is a daunting

task.

• Knowing what information is needed

to select the right style of pump.

Recommendations:

Look carefully at what you need from

your pump. Every type of pump has

its own set of advantages and

drawbacks.

When you have a strong set of

requirements for your pump, it

becomes much easier to hone in on a

specific pump type.

• Use the pump manufacturer’s

applications services to help you with

your final pump selection.

Pump Selection for Laboratory Scale Fluid Handling

andrews-cooper.com PAGE 1

INTRODUCTION

The number of pump types available has become overwhelming, and most manufacturers’ literature

focuses on the strengths of the product. It can be difficult to find literature that clearly describes the

limitations for each pump type as well as the strengths. Below are some descriptions of pump types that

are frequently used in laboratory scale automated fluid handling with some of their disadvantages as well

as their advantages. We will look at the following types of pumps that are commonly used with

laboratory scale applications:

1. PLDC’s………………………………………………………………………………………………………………………………………….2

2. Peristaltic…………………………………………………………………………………………………………………………………….4

3. Diaphragm…………………………………………………………………………………………………………………………………..5

4. Syringe…………………………………………………………………………………………………………………………………………8

5. Magnetic Drive Impeller……………………………………………………………………………………………………….……10

6. Gear…………………………………………………………………………………………………………………………………………..12

7. Lobe…………………………………………………………………………………………………………………………………………..14

There are many more pump types available, each with specific advantages and disadvantages. This white

paper focuses on some of the types most commonly found in laboratory automation and the information

you should know to make the best selection.

Best Match between Process and Pump

Process Requirements

Practices Flow Stability Pump Location

Pressure Shear Sensitive Fluid

Flammable Fluids Etc.

Pump Type Characteristics

Practices Pulsation or Smooth Flow?

Self-Priming?

High or Low Pressure?

Fluid Shear?

EX or ATEX?

Etc.



Pump Type Characteristics

1. Pressurized Liquid Dispensing Container (PLDC) The simple pressurized container is very familiar to most labs. This

method does not use a pump or a motor, only a pressurized gas and a

suitable container.

There are safety-driven limits on the pressures, container volumes, and

container types for flammable chemicals used for pressurized

dispensing. (Please refer to the container manufacturer’s

specifications and the most current version of NFPA 45 for code

limitations.)

A pressurizing gas such as air, nitrogen, or argon is connected to the

top of the container through one of the cap tubes. (Note that air

should never be used to pressurize a container of flammable liquid.) A

dip tube or a bottom port in the container allows fluid to exit the

container at the pressure supplied by the gas. Typically, the pressures

are very low, often less than 5 psi. Knowing the pressure rating of the

container and properly limiting the pressure supply is critical to the

safety of this method.

Special containers designed for the pressurized dispensing of liquids are available for many of the

standard solvents and chemicals sensitive to exposure to air. These are referred to as PLDC’s (Pressurized

Liquid Dispensing Containers). These returnable, stainless containers are ordered from the chemical

supplier already charged with the chemical. When the containers are empty, they are shipped back to

the chemical supplier to be re-used. Using this method, the chemical container is never opened to the

atmosphere and has a pressure relief valve that prevents it from exploding if over-pressurized or heated.

Advantages:

1. Very simple and reliable system with no moving parts.

2. Pressure can be varied with a pressure regulating device on the pressurization gas supply.

3. Inert gases such as argon can be used to avoid any reaction with active chemicals.

4. Very low-cost.

5. Gives steady, non-pulsing flow.

6. No electricity is required, which is an advantage around flammable chemicals.

7. Many hazardous chemicals are available in containers already set up for pressurized dispensing

with a built-in dip tube and a separate pressurization port.

Figure 1. Pressurized

bottle (image courtesy

of Cole-Parmer)



Figure 2. Pure-Pac II PLDC with Micromatic Valve Coupler (Reproduced with permission from Sigma-Aldrich Co., LLC)

Limitations:

1. You cannot run a recirculating system or reverse flow with the basic layout of this method. The

fluid will not flow back into the container without a pump or a reverse pressurization.

2. Be very careful of the combination of container type, pressure regulation, pressure relief, and how

it is controlled. A glass bottle filled with a flammable or toxic fluid with a 20-psi burst pressure

connected to a 2,000-psi nitrogen bottle is an obvious hazard. The dispensing system needs to be

set up with safety in mind with respect to the pressure rating of the container, the pressure

available, and an overpressure relief system vented to a safe location.

3. You must have a source of pressurized gas. If it needs nitrogen or argon and the lab is not piped

with the required gas already, dealing with bottled gasses can add some hassle to the operation.

Ensure the regulators are appropriate for the pressure range you intend to work in. A 2,500-psi

regulator and gage should have a secondary regulator system if you intend to be working with 5

psi in your PLDC.

4. If used in an automated system, the emergency stop function should be set up to dump the

pressurized gas from the container to prevent extended leakage from occurring. The gas released

from the container may contain flammable or toxic fumes, so care must be taken with the

handling of the released gas. Depending on the quantities and hazards of the fluids, system leak

detection may need to be installed and be tied in to the emergency stop system.

5. If using flammable fluids, pay close attention to the grounding requirements. Review the

potential for static electricity generation and discharge throughout your system.



2. Peristaltic Pumps Peristaltic pumps are a top choice for high purity

systems. The pump works on the exterior of a

flexible piece of tubing. This means there is a

straight flow path for the fluid, it never leaves the

tubing, and the fluid contact piece can be cleaned,

sterilized, or replaced easily.

Advantages:

1. Cleanest flow path of any pump – lowest

potential for contamination of the fluid

and ability to easily change out the tubing

for a clean section if needed.

2. Positive displacement pump. Knowing the

number of cycles of the pump allows you

to know how much fluid has passed.

3. Able to handle high-viscosity fluids.

4. Can be self-priming.

5. Many well-developed units are available

with built-in controllers.

6. Flow is easily reversible.

Limitations:

1. Not only can the tubing be replaced, it

MUST be replaced on a regular schedule.

2. Worn tubing can crack and leak as well as

release particulates into the fluid. If you

have a hazardous fluid, assume leaks will

eventually happen. Leak detection may be

needed.

3. Flow from a standard peristaltic pump has

significant pulsation. Different designs are

available with higher numbers of rollers,

multiple out-of-phase roller sets on

parallel tubing, asymmetric roller paths, or

pulse dampeners to reduce the pulsation.

4. Be careful with flow sensors and flow

switches. The pulsating flow causes

problems with many flow sensors.

Monitoring flow from the pump controller

counting revolutions is often more reliable

than a traditional flow sensor.

Figure 3. Peristaltic Pump (Image courtesy of Cole-Parmer)

Figure 4. Peristaltic Operation (image courtesy of Cole-

Parmer)



3. Diaphragm Pumps

Air Operated Double Diaphragm (AODD) Pump

The operation of the AODD pump is described below:

Figure 7. AODD pump operation description from www.versamatic.com, adapted from Samtar on Wikipedia

Figure 5. Plastic AODD Process Pump (image courtesy

of SMC Corporation)

Figure 6. AODD (Image courtesy of SMC Corporation)

http://www.versamatic.com/



The AODD pump is a favorite for many reasons. It is a very flexible system that gives it a significant list of

advantages:

1. It is air operated. It can operate without any electricity at all. Removing a potential ignition

source is ideal when working with flammable fluids. Most designs are intrinsically safe, meaning

they will not generate sparks or enough heat to cause ignition, and can therefore be used with

flammable chemicals.

2. Many chemical pumps do not like pumping air, they rely on the liquid flow to cool bearings.

Without liquid, they quickly overheat. The AODD, however, can be pumped dry without damaging

it.

3. The AODD is self-priming. Unlike most impeller type pumps, you do not have to fill the system

with liquid to make it start pumping. You can have lines completely full of air leading to your

liquid source, and the AODD will handle it no problem if the suction required is within the pump

vacuum capacity.

4. The pump can be deadheaded (attempting to run the pump with the outlet blocked) with no harm

to the pump.

5. The outlet fluid pressure of the AODD is directly proportional to (and usually directly equal to) the

inlet air pressure. Is 60 psi too much for your process? Turn your air pressure down to 20 psi! Do

you need more? Turn your air pressure up to 100 psi! (Note that air pressure changes will affect

pumping speed as well, and pumps will have limits to the air pressure you may safely apply.)

6. The speed of the AODD can be modified to some extent by controlling the rate of air flow into the

pump with a simple needle valve. Less air flow means the pump will move slower.

7. The AODD is a positive displacement pump. By counting the strokes, you know how much volume

has been moved through the pump. Although it is not quite as accurate as a piston pump or a

syringe pump, the accuracy is enough for many applications.

8. You can start and stop the pump as often as you want. There is no motor to overheat with

multiple starting cycles.

9. The pump has very low fluid shear. Fluid shear is important in many coating mixtures and

sensitive chemicals.

10. The AODD will pass solid particles and slurries through it. Sharp particles will eventually damage

the check valves and wear the diaphragms, but it will pump just about anything that can make it

through the entrance and exit ports. One large pump from Wilden is rated to pass 2” diameter

solids through it.

11. There is a huge variety of materials and sizes available in this pump style. Exotic plastics and

rubber compounds are available to handle the most corrosive chemicals, and the least expensive

materials are available for low-cost applications. AODD’s are available with single stroke volumes

down to 5 ml and up to more than 5 liters.

12. The pump is relatively low-cost depending on the materials selected. In general, because there is

no motor it is frequently less expensive than the equivalent motor driven pump. PVDF, PEEK, and

316SS bodies are obviously more expensive than polypropylene or nylon bodies.

13. The pumps can be set up with automatic shuttling air valves that cycle the pump as fast as it can

go, or you can control the air ports and shuttle the pump one cycle at a time for dosing.



However, no pump is perfect! The limitations for using AODD pumps include: 1. Pulsating flow. The flow is based on the diaphragm’s reversal of direction. Every time it strokes,

you get flow. At the end of the stroke, there is no flow. This means a heavy pulsing to your flow. If a high inlet pressure is used with no restriction to the air flow and the outlet is low pressure, the pulsation can be quite violent to the point of shaking fittings loose and cracking plastic tubing supports. The shaking can be carried through the piping around the machine, which is a severe problem for vibration-sensitive processes. Pulsation dampening devices and pressure regulators are sold that do reduce the pulsation and shaking after the pump. The bladder types are large and bulky. Either type can add significant cost depending on the materials required by your chemicals.

2. The pulsating flow can cause waves in process baths where they are often not wanted. 3. The pulsating flow can wreak havoc with flow sensors. Be very careful with specifying a flow

sensor on a system using an AODD pump. You may be better off counting the strokes of the pump to know your flow rate.

4. You cannot reverse the flow direction in the pump. 5. Although the pump depends on ball check valves to operate, I have often found that the check

valves in the pumps will leak and allow backflow when they are turned off. If backflow is a problem, you should consider installing separate check valves outside of the AODD.

6. Most AODD pumps do not fully drain. There is almost always some liquid left in the pump. If you are servicing an AODD that has been used with hazardous fluids, expect to find fluid inside the pump when you disassemble it. It should only be disassembled in a safe place like a flow hood using PPE if it has been used with hazardous fluids.

7. The diaphragms and ball check valves do wear out. The more abrasive particles passed through the pump, the quicker it will wear out.

8. The flow rates can be inconsistent. Changes to inlet/outlet conditions or to the incoming air pressure and flow will have a direct effect on pumping speed.

9. The AODD pumps are generally noisy.

3.1 Electric Diaphragm Pumps

Electric diaphragm pumps can be motor or solenoid driven. They share most of the characteristics of the

AODD pumps above but operate with electricity instead of air. Many laboratory styles are available with

or without controllers. Single and double diaphragm types are available. Single diaphragms have a more

noticeable pulsation, but can deliver accurate dosing down into the microliters depending on the pump.

Figure 8. SMC LSP Solenoid Operated Single Diaphragm Pump, available from 5 to 200 microliters per shot (image courtesy of

SMC Corporation)



Figure 9. Masterflex Single Diaphragm Motor Driven Chemical Dosing Pump (image courtesy of Cole-Parmer)

4. Syringe Pumps Syringe pumps are exactly what they sound like. They typically utilize a standard medical-type glass

syringe body that can be removed/replaced from the drive mechanism. Most syringe pumps are screw-

driven stages that can push or pull on a standard plunger in the syringe. Glass syringes generally give

higher accuracy than a plastic syringe body, and are commonly used.

Figure 10. Single Syringe pump (image courtesy of Cole-Parmer)



Figure 11. Multi-Syringe Pump (Image courtesy of Cole-Parmer)

Advantages:

1. Useful for tiny flow rates, generally used for microfluidics.

2. Many of these devices can use multiple sizes of syringes, so different volumes and flow rates are

available based on the syringe body diameter.

3. Many syringe pumps can reverse and pull fluid back into the syringe.

4. Can get very tight control on flow rates, often less than 1% flow variation.

Limitations:

1. Standard syringe pumps have flow stability problems at low speeds. Proper syringe size for the

flow rate is needed to keep stability.

2. The volume to be pumped is limited by the volume of the syringe.

3. Most pumps are driven with a stepper motor. On low-flow applications, motor steps can be seen

in the fluid flow.

4. The pressure is not controlled and can build up if the flow path is restricted. Pressure is limited by

the slipping torque of the stepper motor. Be aware of what potential pressure can be generated

if the pump is deadheaded.



5. Magnetic Drive Impeller Pumps Impeller pumps in general are the workhorses of the pumping world. The focus here is on the Magnetic

Drive variety (often referred to as Mag Drive) because they have a very important advantage: the fluid

path can be completely sealed from the motor, so there is no leak path from the pump head into the

motor as seals wear out. With hazardous fluids, this can be a crucial advantage.

Figure 12. Sealing, standard impeller pump (top) vs. mag drive pump (bottom)

(Images courtesy of Finish Thompson, Inc.)



Advantages:

1. Impeller pumps give a smooth, consistent flow and can have relatively quiet operation.

2. The motor on a magnetically driven pump is very well protected against leaks, and can even be

mounted on the opposite side of a bulkhead from the pump head and the chemical process area.

3. Available in an almost infinite variety of sizes, shapes, materials, flow, and pressure

characteristics. There are specialty impeller pumps designed for an amazing variety of

applications.

Figure 13. Finish Thompson Mag Drive Impeller Pump (image courtesy of Finish Thompson, Inc.)

Limitations:

1. Impeller pumps are not capable of reversing the flow.

2. High fluid shear at the impeller tips can damage sensitive fluids such as coatings. If you are

pumping a viscous coating or a complex chemical, check with the manufacturer of the chemical to

ensure there is no shear sensitivity with your fluid.

3. Impeller pumps can heat fluids, especially if they are run deadheaded or if the fluid is highly

viscous.

4. Cavitation can be a problem. Use your pump distributor to help you avoid this problem. Make

sure they understand exactly what fluids you will be pumping and the inlet conditions of the

pump.

5. There are special designs for special cases. If you need one of these characteristics, ask your

vendor specifically for it:

a. “Run Dry” capability. Many designs will destroy themselves if run without liquid as they

rely on the passing fluid to cool the bearing sets. There are other pumps like the Finish

Thompson shown in Figure 12 that are designed to survive running dry. If your pump

cannot run dry, we recommend protecting it with a switch to ensure fluid flow is occuring.



b. Suspended Solids. Running solids and grit through a pump may destroy some very

quickly, but there are impeller pumps designed specifically to handle suspended solids.

c. Self-Priming. In order to start a pump that is pulling liquid up from below itself, an

impeller turning in air cannot create enough suction to pull water into the pump. Self-

priming pumps use a reservoir of liquid that recirculates in order to get the pumping

started. This type of pump is not usually applicable to laboratory applications. If you

need a pump that does not require priming, other pump types like the gear, diaphragm,

or peristaltic pump may be a better choice if your process can handle the pulsating flow.

d. EX or ATEX rating. Many pumps are available with ratings to handle flammable fluids or

operate in a potentially explosive atmosphere. Most use special sealed motors and

require special wiring practices to isolate the opportunity for a spark.

e. Duty cycle. Not all motors are made for constant starting and stopping. Others are rated

for this type of use. The important point is to make sure your pump vendor understands

your application. If you are going to be turning the pump on and off constantly, they can

often install a different motor on the pump head that can handle the duty cycle.

6. Fluid can backflow easily through most impeller pumps. Plan on using check valves or normally

closed process control valves if backflow through an unpowered pump creates problems.

6. Gear Pumps There are multiple gear pump designs. They are primarily used for delivering very high pressures or pumping highly viscous fluids. Three types of gear pump designs are shown in Figure 14 below. In general, gear pumps work by using two intermeshed gears to pull fluid into an expanding cavity between gears as the teeth separate. When the fluid reaches the point where the gear teeth come together, the mating action of the gear teeth compress the fluid and push it out a port in the housing.

Figure 14. Gear Pump Designs (image from Wikipedia)



Figure 15. Gear Pump with motor, and disassembled view of pump head (images courtesy of Unibloc-Pump, Inc.)

Advantages:

1. Gear pumps are ideal for pumping high-viscosity fluids that will not flow well through a standard impeller type pump. The oil pump in most automobile engines is a gear pump.

2. Gear pumps are very compact and are generally smaller than impeller pumps. 3. They deliver smooth, controlled flow. 4. Gear pumps are usually self-priming. 5. Gear pumps are positive displacement, so by knowing the number of revolutions, you will know

how much fluid has been pumped (assuming no air is present in the line). 6. Gear pumps are capable of very high pressures, into the thousands of PSI. 7. Reversible flow is possible simply by reversing the direction of the motor.

Limitations:

1. This pump type places a high shear on the fluid, although not as high as impeller pumps when

operating at the same pressure delta.

2. Most cannot run dry for extended periods without damage.

3. Avoid deadheading (blocking the outlet while running the pump).

4. Cannot handle suspended solids, slurries, or abrasives.

5. The gears and the mating housing will wear over time, releasing fine particles into the fluid

stream, reducing the performance of the pump. If you have a process that cannot contaminate

the fluid in any way, be very careful about gear pumps.

6. Can heat fluids.

7. Although EX and ATEX rated versions are available, it is expensive due to the need for an

explosion proof motor and the associated wiring.

8. Fine particulates can be generated by the gears meshing with each other over time.



7. Lobe Pumps Lobe pumps are similar in many ways to gear pumps, but the lobes do not actually contact each other like

the gears in a gear pump. The gearing between the lobes happens outside the pump head and two

separate shafts extend into the pump head, one for each lobe. Because the shafts are cantilevered, a stiff

shaft and a good set of bearings is critical to being able to maintain a tiny clearance between the lobes.

The smaller the clearance between the lobes, the less backflow occurs between the lobes and the more

efficient the pump is. Lobe pumps can be made in very cleanable configurations. They are one of the few

pumps that lends itself to pharma and food CIP and SIP (Clean In Place and Steam In Place), and so are

very well-suited to use in biopharma projects.

Figure 16. Lobe Pump with controller, and disassembled view of a pump head (images courtesy of Unibloc-Pump, Inc.)

Advantages:

1. The basic design is relatively free of crevices and places to trap fluid, meaning the pump is easily cleaned compared to most other pump designs. Most can be disassembled for cleaning, or can even be cleaned using pharma CIP or SIP procedures without disassembling the pump at all.

2. Because the lobes do not contact each other, there is lower probability of fine particulates being generated as can happen in an aging gear pump.

3. The pump design is low shear by nature and is very gentle on the fluid. 4. The pump can pass solids. 5. Lobe pumps deliver smooth, controlled flow. 6. Lobe pumps are capable of up to 90 psi pressure rise across the pump. 7. Reversible flow is possible simply by reversing the direction of the motor. 8. Most designs can run dry for at least a period of time and will handle some air or gas bubbles

coming through the system.

Limitations:

1. Self-priming ability is limited.

2. Low viscosity fluids will have a higher leakage rate between the lobes, meaning the pump

efficiency decreases with a lower viscosity fluid.

3. Avoid deadheading (blocking the outlet while running the pump).

4. Can heat fluids if deadheaded, but it is more gentle than a gear pump.

5. Although EX and ATEX rated versions are available, it is expensive due to the need for an

explosion proof motor and the associated wiring.



Conclusion Finding the best pump type for your particular application requires a specific knowledge of your process

and the fluid. To aid in the selection of the right pump for your project, start by finding answers to the

following questions:

In addition, having a Process and Instrumentation Diagram (P&ID) of your proposed system will help you

think through the needs of the system and better communicate the process requirements for the pump.

Utilize fluid handling experts to review your information to ensure you get the pump that best matches

the process needs.

Andrews-Cooper draws upon years of experience designing and building laboratory scale automated fluid

handling systems. Give us a call to discuss your application and challenges!

1. What flow rate do you need?

2. What is the viscosity of the fluid?

3. What is the head pressure you will

pump against?

4. What is the head pressure available at

the pump inlet?

5. What is the vapor pressure of the

fluid?

6. What is the temperature of the fluid,

and is the fluid sensitive to heating?

7. Do you need the pump to self-prime

or handle gas bubbles?

8. Do you need to reverse flow?

9. Is the fluid flammable, corrosive, or

have specific material contact needs?

10. Is the fluid shear sensitive?

11. What pressures can you work with?

12. Is the process sensitive to

contamination?

13. Do you have solids in your liquid? If so,

what size and what are the solids?

14. Do you care about pulsation or noise?

15. How accurately do you need to control

flow rate or volume?

16. Are you passing the fluid through once,

or recirculating?



ABOUT ANDREWS-COOPER

Andrews-Cooper was founded by two engineers who worked for a major manufacturer of medical

devices and consumer products. Since 2000, Andrews-Cooper has excelled in product design for the

development of both medical devices and consumer products. As a result of working closely with

manufacturers of these products, Andrews-Cooper also branched out almost immediately into

automation equipment. Andrews-Cooper officially started an Automation Division in 2008. The design

process at Andrews-Cooper is backed up by an ISO 9001 and 13485 compliant Quality Management

System.

Andrews-Cooper has built a business focused on solving real engineering problems. Our deep experience

and diverse expertise allow us to serve our customers at the highest level. We have found that a

partnership approach is the best way to ensure the job is done right. We offer this paper to stimulate

conversation as to how best to help our customers as they automate fluid handling processes.

For more information on how A-C can help, please visit our website at www.andrews-cooper.com, or

contact us directly.

Bruce Smith is the Applications Engineering Manager at the

Andrews-Cooper Automation Division. He has been challenged

with the handling of flammables, acids, reactive chemicals, high

toxicity chemicals, UV sensitive chemicals, and shear sensitive

coatings as well as adhesives, lubricants, and DI water during a

wide variety of automation projects.

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