Advantage Hydra-Cell Pumps · the Hydra-Cell pump Each of these is generically different from other types of pump. With the exception of the Hydra-Cell, which is manufactured by Wanner

Chemical Engineering World�JANUARY 2007�73

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How do you reconcile

the need to constrain

pump costs with the

need to avoid pump

failure? Dr Ing

Friedrich-Wilhelm Hennecke, former

pump chief at BASF and a leading

authority on process pumps, gave

some good basic advice when

interviewed by this journal last year

(CEW June 2006).

"A company can save money," he

said, "by buying cheap pumps and doing

no maintenance. At least for a short time,

for long-term this will cause high costs

for repairs and loss of production. The

best way is to select the right pump (flow

The importance of pumps in the world of chemical processing and manufacture is self-evident. Many

processes cannot run without them. The cost of pump failure in downtime and lost production, also in

some cases worries about safety, may be very high. Costs associated with the pump itself - not only

buying the pump and standby, but operational costs such as energy consumption, maintenance, repairs

and replacement, may be far from negligible

Advantage Hydra-CellPumps

rate, head) of good quality and run it

properly, with regular maintenance."

There is certainly plenty of choice.

At the Achema exhibition in Frankfurt

in May 2006, for example, no fewer

than 160 suppliers were offering their

products in the halls devoted to process

pumps.

However, selection is not always

easy. In the more straightforward

applications where (to take an ideal set

of conditions) the liquid to be pumped

is clean water at ambient temperature

and the operating pressure is no more

than about 10 bar, many types of pump

could perform satisfactorily.

Choice will probably be governed

by cost but even in these conditions,

according to Dr Hennecke, this should

never just mean purchase cost. The true

cost of a pump, defined as Life Cycle

Cost (LCC), is the total cost of the pump

from purchase to scrapping. This will

include purchase of the pump, motor

and auxiliary devices, installation and

commissioning, energy consumed

during the lifetime of the unit,

supervisory labour costs, maintenance,

repair, downtime and consequential

loss of production, environmental cost,

decommissioning and disposal.

In practice some of these elements

(e.g. downtime) are very difficult to

calculate in advance, while one or two

others may not be significant. But costs

such as energy, maintenance and repair

can be crucial in assessing LCC and

making sensible comparisons between

one type of pump and another.

The concept of life cycle costs is one

of Dr Hennecke's ongoing interests.

While still at BASF, he co-edited the

landmark 'Guide to Pump Life Cycle

Costs' published jointly in 2001 by

Europump and the Hydraulic Institute

in the USA. In 2005 he carried out a

comparative investigation into the

lifetime costs of five different types

of pump, presenting the results in

March 2006. Four of these pump types

are well known in the process

industries. The fifth type, viz., the

Hydra-Cell is less well known, but inFigure 1: Pump life cycle costs (LCC), comparison example (pumps recommended for 1.4 m3/hr

flow rate) F-W Hennecke March 2006

LCC comparison survey (1)


PROCESS

some respects it is the most

remarkable, and in many applications

it has proved a valid and less costly

alternative to types of pump more

familiar to plant engineers.

The types of pump considered by

Dr Hennecke were:

the centrifugal pump

the side-channel pump

the peristaltic pump.

the membrane piston pump

the Hydra-Cell pump

Each of these is generically different

from other types of pump. With the

exception of the Hydra-Cell, which is

manufactured by Wanner Engineering,

all the types investigated are produced

by more than one company.

For his comparative study, Dr

Hennecke approached a prominent

manufacturer of each type, requesting the

company to select its most appropriate

model for given operating requirements

in three flow capacities. Also to supply

data on routine maintenance needs,

expected time between repairs, costs of

spare parts and labour. All the

information was provided by the pump

manufacturers themselves.

The scope of the investigation covered

flow rates of 1.4, 4.2 and 8.4m3/hr and

pressures of 5, 10, 50, 75 and 100 bar. In

practice, not all the pump types are suited

to operation in all circumstances.

Figure 2: Hydra-Cell pump - simple construction

Limiting factors include pressure,

temperature, solid content, hazardous

fluids and pump pulsation.

Dr Hennecke's research into LCC was

very detailed (a full copy of his report,

published in the journal Paper

Technology, may be downloaded from

the Wanner International web site

www.wannerint.com). Among its

general conclusions he noted that the

Hydra-Cell was the most economic

pump overall 'within the pressure and

flow ranges considered.' And it was

not restricted by pressure considerations

or the type of fluid it could handle. The

side-channel pump was comparable,

within its pressure range, but could only

handle clean fluids.

"The LCC of the peristaltic pump",

he commented, "is increased by its high

consumption of replacement tubes",

while "Membrane piston pumps are very

efficient, but their investment cost and

the cost of spare parts and labour when

changing membranes are extremely

high". Centrifugal pumps "are for low

pressures and high flow rates".

For pressures above 10 bar,

irrespective of flow rate, only positive


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displacement pumps were considered

suitable, ruling out centrifugal, side

channel and peristaltic types. The

results showed that for these higher

pressure applications the LCC of the

Hydra-Cell pump was substantially

lower in each case than that of its only

real alternative, the membrane piston

pump (see Figure 1).

The basic Hydra-Cell design, which

today is embodied in a range of models

covering flows up to 138 litres per

minute (8.3 m3/hour) and discharge

pressures up to 170 bar, originated in

the 1970s. It was then that William F.

Wanner built his first seal-less pumps

and joined with his son Bill, current

CEO, in founding the company that

remains the sole manufacturer.

From the outset William Wanner

determined to keep his design simple

and also avoid the use of dynamic

seals. He was targeting certain

markets and applications and knew

that seal wear was one of the most

common causes of failure and high

repair costs for existing positive

displacement pumps more especially

when they were handling chemicals

and liquids carrying abrasives.

Since these early days, the

company has invested massively in

design, development and

sophisticated manufacturing

technology. These programmes

continue more strongly than ever. But

Figure 3: Hydra-Cell G25 pump delivering hot de-ionised water to control temperature in steam line

the original concept still holds good.

The Hydra-Cell pump (Figure 2)

has no dynamic seals. It uses the

principle of hydraulically balanced

diaphragms, most models in the range

have 3 or 5 diaphragms in a single

head, producing a flow with very low

pulsation. The diaphragms have a dual

function. They are flexed in sequence

from behind by liquid pressure in the

hydraulic cells to provide the pumping

action. They also act as a barrier, totally

isolating the oil in the drive end of the

pump from the chemical or other

liquid being pumped. This allows the

pump to handle many 'difficult' media

including corrosives, abrasives,

liquids with solids in suspension,


PROCESS

viscous products and thin non-

lubricating liquids. The relatively few

components in contact with the liquid

medium, viz., pump head, diaphragms,

inlet and outlet valves are offered in a

wide range of suitably resistant

materials.

But tolerance of media is rarely the

only consideration, and the Hydra-Cell

pump has other valuable features. Any

pump vulnerable to seal wear, or

whose pumping action depends on

narrow clearances between moving

surfaces, begins with a disadvantage

when handling certain types of liquid.

In the cement industry for example,

xylene (a by-product of wood and coal

processing) is pumped to burner

nozzles to be used as fuel. But it is toxic,

non-lubricating and contains abrasive

particles. It is not easy to pump.

Cement plants tried various pumping

solutions. A gear pump with good

quality seals lasted for one week.

Piston pumps also failed, and the

required working pressure (25 bar)

was too high for peristaltic pumps.

Traditional metering pumps (hydraulic

diaphragm pumps) could handle

xylene, but pulsation would have been

a problem and in any case the cost of

those elaborately engineered pumps

ruled them out for this application.

As often happens, what made pump

selection difficult was having to satisfy

several potentially conflicting

requirements simultaneously:

pumping abrasive liquid that would

damage seals; avoiding toxic leakage;

pumping at pressure; delivering a

smooth, even flow; ensuring reliability

and satisfactory service life-and all

without procuring at uneconomic

prices.

Pumping xylene safely, with no risk

of seal leaks, is no problem for the seal-

less Hydra-Cell G25 pump; and the

specified delivery pressure of 25 bar is

well within the G25's pressure

capability of 70 bar. Moreover, the G25

incorporates 3 sequentially-acting

diaphragms within its single compact

pump head, so that the steady stream

of product delivered to the nozzles at

50 l/min is virtually pulse-free, with

no need for pulsation dampeners.

Proven reliability and their good low-

maintenance record provide further

evidence of why the cement industries

of several European countries continue

to rely on G25 pumps for this work.

Wanner engineers are sometimes

asked how the flexible diaphragms of

the Hydra-Cell cope with the high

operating pressures to which they are

exposed. The answer is that in normal

operation the diaphragm never sees

more than 2 psi pressure differential.

Hydraulic balance is maintained

between the fluids on either side of the

membrane, so that the diaphragm itself

comes under no stress even at high

working pressures. A development by

Wanner adds a further safeguard to the

Hydra-Cell design. Its patented Kel-Cell

technology protects the diaphragms

from rupture under adverse inlet

conditions such as the severe vacuum

that might result from the accidental

closure of a valve, or a suction filter

becoming blocked. The pump can run

dry indefinitely without damage.

The drive mechanism, submerged

in a reservoir of oil, is permanently

lubricated and this arrangement means

that power is transmitted through the

drive train with minimal friction losses

helping to account for the efficiency of

the pump. The Hydra-Cell achieves

efficiencies as high as 85 per cent,

compared with 45 per cent for a typical

centrifugal pump. In consequence, the

pumps can often be fitted with a motor

smaller than would be needed for pumps

of another type for the same work

output. Energy savings alone have

enabled plants to recover the cost of a

Hydra-Cell pump within a year.

With their high efficiency and simple

build-multiple diaphragms concentrated

in a single head, Hydra-Cell pumps are

remarkably compact in relation to their

performance. Pune-based Comp

Engineering & Export, a leading Indian

manufacturer and exporter of spray

drying systems, cites the small size and

low weight of the Hydra-Cell, as well as

its proven trouble-free operation, as

important considerations when

choosing to fit Hydra-Cell pumps as

original equipment in its spray dryers.

Operating pressures for these systems

are generally between 30-50 bar.

Products sprayed include slurries and

soap solutions and typical flow rates are

from 15 to 50 l/min. Models most

Figure 4: Pulsation comparison Hydra-Cell G10 v. Traditional metering pump (single head)


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frequently fitted are the Hydra-Cell G10

and G25, though occasionally a lower or

higher flow rate Hydra-Cell pump has

been used. No problems have been

experienced and recently there has been

some interest from customers of Comp's

sister company Mojj Engineering

Systems, which makes similar

equipment for the Indian market.

Proven applications of Hydra-Cell

pumps in the process industries are

numerous and diverse. As well as spray

drying they include reverse osmosis,

gas conditioning and cooling (Figure

3), pressure cleaning of filters, tanks

and mixing vessels and transfer of

product from storage tanks directly

into process lines.

Worldwide, a rapidly-growing area

of application for Hydra-Cell pumps is

metering and dosing. Hydra Cell pumps

have long been used in this field for a

variety of reasons, and it was not at first

noticed that on more and more

installations the pump had been chosen

for its ability to deliver liquid in precise

volumes. This trend was happening at

the same time as rapid advances were

being made in electronic control devices.

Frequency inverters, for controlling the

speed of an electric motor,

simultaneously became far more

accurate and less expensive.

The essential point here is that the

flow of a Hydra-Cell pump is directly

proportional to pump speed and that this

relationship is linear, exceeding the API

675 performance specification. In practical

terms, it has become simple and

inexpensive to automate a metering

operation, while taking advantage of

other Hydra-Cell features such as low

pulsation. Compared with traditional

metering pumps the Hydra-Cell has

virtually pulse-free pulsation (Figure 4).

Traditional (piston diaphragm)

pumps built to comply with the API 675

standard have long been regarded as the

'true' type of metering pump. API 675 laid

down standards of accuracy for metered

flow, and also defined the construction

features which were then judged the best

means of setting, sustaining and re-

adjusting flow within precise limits.

But the basic technology is outdated and

the resultant engineering is elaborate.

Inevitably such pumps are big, heavy and

expensive (Figure 5).

To vary flow, they have an inbuilt

mechanism that changes the actual or

effective length of the piston stroke.

Costly to automate, by adding an

actuator, they are relatively slow to react

to external signal.

Two Hydra-Cell G10 pumps replaced

a traditional single-piston metering

pump delivering de-mineralised water

with 30 per cent titanium dioxide into a

process line at a German chemical plant.

Plant engineers had considered replacing

the original pump with a triplex (3-

headed) pump to try to reduce pulsation,

but the two Hydra-Cell pumps had

overwhelming advantages. Pulsation is

much lower, and even together they took

less space, were cheaper to run, consumed

less energy and cost less to buy. And the

control system is simple. A flow meter

monitors the process line, passing data to

a computer, which controls the speed of

the pumps via a frequency inverter and

their drive motors. Flow is varied

instantly and accurately on signal.

Last year Wanner launched 'Hydra-

Cell Metering Solutions', a new series of

Hydra-Cell based pumps and control

accessories specifically for metering and

dosing applications. The company also

announced the results of a 2-year

programme of tests under controlled

installation conditions. They showed

that all the pumps (including the basic

Hydra-Cell models) consistently

exceeded API 675 standards for Linearity

+/- 3 per cent, repeatability +/- 3 per

cent and steady state +/-1 per cent. Full

documentation is available.

For more information:

Hydra-Cell Pumps

Sales and technical support in India

Machinomatic Engineers, 102 Naigara

Near Colaba South Post Office,

Mumbai - 400 005,India

Tel: +91 22 22 151 063

E-mail: [email protected]

Figure 5: Size comparison Hydra-Cell G10 v. Traditional metering pump

Performance (both pumps) Max flow: 1500 l/hr Max pressure: 80 bar

Documents

Advantage Hydra-Cell Pumps · the Hydra-Cell pump Each of these is generically different from other types of pump. With the exception of the Hydra-Cell, which is manufactured by Wanner