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Kriebel Engineered

Equipment Ltd. is a full-

service manufacturers’

representative firm

serving the process

utility and food

industries in eastern PA

southern NJ and DE.

 August 2004

 Volume1, Issue 3

Keeping Engineered Equipment Living

Metering pumps are positive displacement

machines that use a diaphragm in combina-tion with suction and discharge check valves

to pressurize and move a fluid. Just about

every industry that uses liquids has a meter-

ing pump or two tucked away somewhere,

even if only to inject water treatment chemi-

cals.

Types of Metering Pumps 

Quite simply, metering pumps are either me-

chanically or hydraulically actuated. In a me-

chanical pump, the diaphragm and the drive

unit are physically connected. In a hydrauli-

cally actuated pump, the diaphragm is actu-

ated by pressurized hydraulic oil.

Both types of pumps can be further classified

by their method of volume control: either lost

motion or amplitude

modulation. In an

amplitude modulated

machine, the actual

stroke length of the

diaphragm is ad-

 justed by means of a

variable cam and

gear arrangement.

Horsepower requirements will therefore in-

crease and decrease with flow. A lost mo-

tion machine will utilize mechanical stops,

springs or a hydraulic bypass without actu-

ally adjusting the travel of the cam; horse-

power consumption remains constant.

Mechanically Actuated

The first metering pumps were mechanically

actuated. Typically, these pumps are applied

in low-pressure, high-flow applications. Ac-

curacy of mechanically actuated metering

pumps varies between 1-2% depending on

manufacturer and model.

Mechanically actuated pumps can either be

driven by a solenoid, a gear drive or pneu-

matic cylinder. Solenoid pumps are limited

to the smallest power requirements, typically

less than 1/10 hp.

A low cost alternative, bellows pumps are

used predominately in low flow, low pressure

applications.

 www. kriebel-ltd.com e-mail: sales@kriebel-ltd.com© 2004

Kriebel Engineered Equipment, Ltd

Looking for a Metering

Pump? Explore Your Options

 Solenoid, mechanical, hydrau-

lic – what does it all mean?

Does it matter?

 A high-performance, state-of-the-art, amplitude modulation

metering pump.

St r a ig h t en ing o u t yo ur p r o cess p r o b l em s

 A solenoid metering pump.

8/20/2019 Metering Pump Engineered

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140 Ivy Lane

King of Prussia, PA 19406

Phone: 610-337-8995

Fax: 610-337-8996

Email: sales@kriebel-ltd.com

duty, including accuracy requirements, is

extremely important in selecting a metering

pump. Proper system design is also impor-

tant, and will be addressed in a later issue.

In general, bellows pumps are used in low

flow (less than 1 gpm) and low pressure

(under 50 psig) applications. Up to 3 heads

can be combined in a single pump.

Solenoid pumps typically are used in flow

conditions less than 10 gph and less than

200 psig. Both bellows and solenoid pumps

are considered “throw-away” pumps in that

it is easier and cheaper to replace the pump

than repair it.

For flows up to 600 gph, one of three pumps

can be selected depending upon the particu-

lar technology requirements: mechanically

actuated, lost motion; hydraulically actu-

ated, hydraulic bypass; or hydraulically actu-

ated, amplitude modulated.

Conclusion

The world of metering pumps encompasses

applications from drops per hour up to 100

gpm, with pressures nearing 10,000 psi.

With a basic understanding of the different

types of metering pumps, you’re on your way

to selecting the right one for your applica-

tion.

For more information

For help selecting your next metering pump,

call us at 610-337-8995.

Look for the next issue of KEEL to appear on

our website in September. Or register to

have the next issue delivered to you.

Hydraulically Actuated

Hydraulically actuated pumps have one of

two methods of control: amplitude modula-

tion or hydraulic bypass. Hydraulically actu-ated amplitude modulation pumps operate

in the same fashion their mechanically actu-

ated counterparts: by varying stoke length.

Bypass machines vary the flow of hydraulic

fluid to the backside of the diaphragm to

control volume or capacity. Thus, capacity

control is adjusted rather than stroke length.

The effect is that the power requirement is

constant because pump technically does the

same amount of work internally whether at

0% or 100%.

Hydraulically actuated pumps are gear

driven and have an accuracy of 0.5-1.0%.

Controlling Metering Pumps

The capacity of metering pumps can be

changed by modifying stroke speed, and/or

stroke length.

Typically, in automated systems, the pump’sstroke speed is varied to change pump con-

trol. In applications where the capacity re-

quirement remains constant, stroke length

can be varied to fine tune pump capacity. If

pump capacity is expected to vary and accu-

racy is important, the maximum turndown

ratio is 10:1 via either stroke length control

or speed control. However, the two can be

combined to provide infinite control of your

metering pump.

Selecting Your Metering Pump

Thorough definition of the pump’s expected

Keeping Engineered Equipment Living August 2004

“With a basic under-

standing of the differ-

ent types of metering

pumps you’re on your

way to selecting the

right one for your ap-

plication

.”

Kriebel Engineered Equipment, Ltd.