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TOTAL ENGINEERING AND MANUFACTURING =
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Conflicting=20
requirements of API 610 mean
the best pump for a job may not =
always be=20
selected
Enquiries=20
for pumps from the oil and gas industries normally refer to API =
610, now=20
ISO 13709, as the minimum technical standard. Often individual =
users and=20
contractors/consultants add their own in-house project =
specifications and=20
standards. Oliver Brigginshaw, Managing Director of Amarinth, a =
company=20
specialising in the design, application and manufacture of pumps =
and=20
associated equipment, looks at this combination of sometimes =
conflicting=20
requirements of specifications and standards and explores why this =
can=20
potentially lead to the best pump for the job not being selected.=20
API 610 has =
some=20
apparently contradictory statements relating to the preferred and=20
allowable operating range and the position of the customers rated =
flow on=20
the pump curve. Preferred and allowable limits are defined as a =
percentage=20
of the designed Best Efficiency Point (BEP). Many supplementary=20
specifications laid down by companies require their rated flow to =
be to=20
the left of BEP which further limits the selectable area of the =
curve. In=20
any event, strict interpretation of API 610 would restrict rated =
flow to a=20
narrow band just to the left of best efficiency flow. =
There is an=20
overriding feeling in the industry that abiding by the rules gives =
better=20
reliability and availability. This may well be the case with high =
specific=20
energy machines (that is motors over 300kW running at more than =
3000 rpm)=20
but is not always applicable to other smaller pumps. It should be =
borne in=20
mind that the rules are of necessity based on historical =
experience and=20
data, derived over long periods of time and often old design =
machines.=20
More recent designs, having evolved from the older designs =
and=20
operating experience, incorporate concepts, philosophy and =
materials such=20
as small rotor deflections obtained by low radial thrust hydraulic =
designs=20
and stiffer shafts (L3/D4). Such design improvements mean that =
some of the=20
historical rules may not be as applicable as they once were. =
Admittedly=20
units with drives greater than 300kW certainly do need more =
attention to=20
operating range and conditions if potentially higher maintenance, =
or worse=20
wrecking of the pump, is to be avoided, as the higher levels of =
energy at=20
the pump inlet and outlet will drive any destructive effects that =
much=20
harder.
Preferred=20
and allowable ranges
API 610=20
defines the operating ranges of the pump curves as a) preferable - =
80% to=20
110% and b) allowable - 70% to 120%, of the designed BEP (Fig 1). =
These=20
limits are also defined for acceptable levels of vibration and to =
limit=20
suction specific speeds aimed at controlling recirculation =
susceptibility.=20
However, this is not clearly defined in API 610 why the 70% to =
120% limits=20
are imposed. Most people think it is to make sure vibration limits =
are=20
maintained and recirculation does not commence, but it is not =
clear why=20
API 610 has this arbitrary rule, which must vary from pump to =
pump.=20
This standard often unduly restricts small lower energy =
units of=20
the OH1 and OH2 type as they can operate well within the vibration =
limits=20
but still be well outside the allowable 70% of BEP. Most pump=20
manufacturers will define a minimum flow for the unit which can be =
as low=20
as 15% - 20% of BEP (see Fig 1). Many pumps can operate very=20
satisfactorily close to minimum flow whilst still achieving the =
API 610=20
vibration limits.
Conflicting requirements =
Such restrictions can lead to application =
selection=20
difficulties for the manufacturer, for example achieving a low =
enough=20
NPSH. If the pump has to be within the 70% - 110% preferable range =
a=20
smaller pump is often needed, but the NPSH available at the =
customer's=20
duty can often be less than the smaller pump requires (see Fig 2). =
If the=20
manufacturer is satisfied that the larger pump can operate close =
to its=20
minimum flow without problems the larger pump would be a =
preferable choice=20
as the NPSH required by the large pump operating well to the left =
of the=20
BEP could be less than the NPSH required by the smaller pump =
operating in=20
the "preferred operating range".
![](3D"http://www.thejournalofindustryandtechnology.biz/img38.jpg")
Breaking=20
down conceptions
In =
addition,=20
there are sometimes additional benefits to the customer of having =
a number=20
of the same size of pump rather than a number of different sized =
pumps.=20
These include interchangeability of parts which helps with service =
and=20
refurbishments, lower stock holding of critical spare parts (e.g. =
one=20
shaft will support three pumps rather than three different shafts =
for=20
three different pumps). Again, staying with the preferable limits =
defined=20
by API 610 often results in more different sized pumps being =
selected to=20
ensure compliance, rather than more of the same pump.
Most =
OH1 and=20
OH2 pumps up to 300kW would not exceed the 12,800 suction specific =
speed=20
limit sensibly introduced by many users. Improved hydraulic and =
mechanical=20
deigns often meet the deflection, vibration and noise criteria =
over a=20
wider flow ranges than the API limits permit. Evidence is =
accumulating for=20
these units to indicate the life of a pump is not impaired by =
operating=20
outside of the preferable limits - that less than 70% away from =
the=20
designed best efficiency.
![](3D"http://www.thejournalofindustryandtechnology.biz/img40.gif")
Most of=20
these units are fairly low specific speed and the value of the =
operating=20
efficiency does not drop off quickly, so operating energy costs =
are not=20
significantly increased. Many of these machines do not run =
continuously=20
and so overall availability is probably more critical to the =
operator. A=20
more flexible standard?
API 610 does recognise the =
limitations=20
imposed on small pumps in the small print but unfortunately many=20
specifications do not allow the flexibility that is needed to =
permit more=20
appropriate selection in the lower energy part of the market. =
Perhaps at=20
the next revision, API 610 could emphasise that for lower energy =
pumps=20
meeting all the design and test criteria, a wider operating range =
than the=20
current preferable operating limits would be acceptable so long as =
the=20
pump is deemed fit for purpose and guaranteed as such by the =
manufacturer?=20
ISO 5199 already recommends that the manufacturer should =
advise=20
the allowable operating range based on their analysis and =
experience of=20
the pump. ANSI/HI 9.6.3 and other ANSI standards discuss the =
factors that=20
should be considered when considering operating range.=20
Breaking=20
down perceptions
Responsible=20
manufacturers with modern designs will always ensure that API 610 =
pumps=20
exceed the vibration, deflection and bearing life requirements of =
the=20
standard and find that on smaller machines all of these limits can =
still=20
be achieved considerably further away from the current 70% from =
BEP=20
allowable limits. Amarinth has experienced pumps operating as far =
away as=20
0% of BEP (i.e. closed valve) on test that are still within API =
610=20
vibration limits (though the pump would of course eventually =
overheat),=20
but manufacturers remain hampered by "industry perception" into =
not=20
offering units outside of the current 70% BEP allowable limits.=20
There are now some more enlightened user specifications =
being=20
issued which are starting to recognise the situation and give =
wider scope,=20
but more detailed definition as to what is permissible and what is =
not=20
would be useful and provide more clarity to the industry. =
At the=20
end of the day the pump manufacturer's job is to make money making =
pumps=20
and dissatisfied customers and warranty costs they certainly do =
not need.=20
If users are to really get the best pump for the job, then =
bringing the=20
wealth of experience of a respected pump manufacturer to bear and =
putting=20
aside "perceptions" during the selection of API 610 pumps could =
deliver=20
significant benefits.
For further information, e-mail:
The ARO Fluid=20
Technologies business of Ingersoll Rand expand its ARO EXP Series=20
portfolio of diaphragm pumps
The ARO=20
Fluid Technologies business of Ingersoll Rand expand its ARO EXP =
Series=20
portfolio of diaphragm pumps with a three-inch ported 2:1 High =
Pressure=20
pump. Available in Stainless Steel, the PH30F is the ultimate =
solution for=20
applications that require the transfer of viscous or high-solids =
fluids at=20
pressures exceeding 6.9 bar. Ideal applications include filter =
press water=20
removal, ceramic slurry injection, and resin transfer.
By =
utilizing=20
the effective surface areas of both diaphragms to double output =
pressure,=20
the PH30F can produce fluid discharge pressures up to 13.8 bar =
while=20
maintaining an industry-leading flow rate up to 590 liters/min. =
The PH30F=20
2:1 is also capable of providing pressure boosts in applications =
where=20
downstream system pressure drop is high, or in situations where =
inlet air=20
pressure is below the desired operating level.
The PH30F=20
offers users all of the trusted features exclusive to the =
ultra-efficient=20
Ingersoll Rand ARO EXP. These features include the patented =
SimulShiftTM=20
and Quick DumpTM valve technologies to ensure stall-free and =
ice-free=20
operation. Additionally, the combination of sturdy bolted =
construction=20
design and long-lasting convoluted diaphragms provides increased =
up-time=20
and unparalleled ease of maintenance.
For further =
information,=20
contact Karina Visciola, e-mail:
Machinery=20
Directive 2006/42/EC section 1.4.22
Machinery=20
Directive 2006/42/EC becomes effective on 29th December this year =
and=20
section 1.4.2.2 covers movable guards which must be associated =
with an=20
interlocking device that prevents the start of hazardous machinery =
functions until they are closed by giving a command whenever they =
are no=20
longer closed. Fortunately for engineers seeking to ensure =
compliance -=20
Elesa's CFS hinge could well be exactly what they=20
need.
Refer =
to the=20
picture: Two variants are available - the CFS-SH with countersunk =
screw=20
fixings for optimum strength and security - and the CVS-CH with =
slotted=20
fixing.
Elesa are=20
well known for their high quality standard machine elements and =
their CFS=20
hinge lives up to that reputation; its specification covers use in =
hazardous area to Cat 1 and works so as to switch off equipment =
when a=20
door or panel is opened. This is a great aid in industrial =
environments=20
where it helps to ensure operator safety. Alternatively the CFS =
may be=20
used to remotely indicate status, e.g. for access monitoring. =
Construction=20
is an integral glass reinforced technopolymer unit ensuring a =
tamper-proof=20
installation and easy assembly.
Two variants are available =
- the=20
CFS-SH with countersunk screw fixings for optimum strength and =
security -=20
and the CVS-CH with slotted fixing for easy adjustment. Each one =
is=20
offered with either top mount cable connection or rear mounting =
connector=20
and appropriate leads to suit either the machine control or status =
indication role.
The CFS switching hinge, normally paired =
with the=20
standard CFM hinge, provides 180=C2=B0 opening with switching =
operation over=20
the range 4=C2=B0 to 15=C2=B0. It meets EN60204-1, EN6097-5-1, =
EN60529 and GS-ET15=20
with the switch and contacts sealed to IP65 - for indoor use. =
For=20
further information, e-mail: