Chemical Engineering World�JANUARY 2007�73
PROCESS
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)
Chemical Engineering World�JANUARY 2007�74
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
Chemical Engineering World�JANUARY 2007�75
PROCESS
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,
Chemical Engineering World�JANUARY 2007�76
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)
Chemical Engineering World�JANUARY 2007�77
PROCESS
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
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