Vacuum Pumps
R 45
Vacuum Pumps
R 45
December 1998
December 1998
SCHOOL SCIENCE SERVICE
CONTENTS
Page
1.
The scope of this guide
1
2.
Water-powered filter pumps
1
3.
Choice of type of pumps
1
4.
Rotary pumps
5
5.
Diaphragm pumps
8
6.
Hand pumps
9
7.
Vacuum for filtration
10
8.
Repair companies
13
9.
Accessories
13
10.
Discounts, charges and addresses
13
This guide replaces L45 Vacuum Pumps (February 1986)
Strictly confidential
Circulation to Members and Associates only
© CLEAPSS 1998
School Science Service
Brunel University
Uxbridge UB8 3PH
Tel:
Fax:
E-mail:
Web site:
01895 251496
01895 814372
[email protected]
www.cleapss.org.uk
R45 Vacuum Pumps
- for vacuum work in physics and filtration in chemistry
1.
The scope of this guide
The following pumps will be included in this guide.
•
Rotary pumps - the most effective but the most expensive and requiring most
maintenance. Maximum price limit on pumps included: £600.
•
Diaphragm pumps - less effective but less expensive and requiring less maintenance. Maximum price limit on pumps included: £250.
•
Hand pumps
Mitivac, pistol-type - capable of evacuating only small-volume, low-leak systems. Prices: £35-60.
Vacu-vin pump - intended for reducing air pressure in partly-empty wine
bottles but of use for vacuum filtration. Prices: around £7.
There is no detailed consideration of oil-diffusion pumps, as they are seldom used but,
for the sake of completeness, they are included in Tables 1 and 2.
This guide should be read in conjunction with section 12.20 of the CLEAPSS Laboratory
Handbook, particularly for information on safety, vacuum techniques and the use and
maintenance of rotary pumps.
2.
Water-powered filter pumps
No detailed consideration is given to water-powered filter pumps in this guide. Water
company codes of practice require that water supplies to laboratories are from a header
tank rather than directly from the mains; this is to avoid any contamination of the water
main due to suck-back should mains pressure fall. These codes are likely to be
supported by legislation now being prepared.
The result is that filter pumps fitted to the water supply, used for filtration for decades,
cannot now be used effectively in many laboratories. It is possible that direct connection
to the main may be allowed through special valves but these are expensive and require
maintenance. Further, in some parts of Britain at least, water is increasingly regarded as
a scarce commodity; use of traditional filter pumps may be regarded as extravagant.
For these reasons, water-powered filter pumps will not be covered in this guide.
section 7 covers alternative means of producing vacuum for filtration. However, if a
school has sufficient water pressure to use these pumps effectively, there is no legal
reason why they should stop using them.
3.
Choice of type of pumps
The type of pump a school purchases should depend on the uses anticipated. The two
main features to be considered are the lowest pressure required of the pump and its
flow rate. Often, when connected to a vacuum system, eg, a bell jar, the lowest pressure
produced by a pump will depend on flow rate, as a high flow will better overcome the
effect of leaks.
Tables 1 - 3 will help with choice of pumps: Table 1 outlines the main performance
features of the different types of pump and Table 2 relates choice of pump to use. Table
3 compares the features of the different pumps.
Table 1
Performance of vacuum pumps
Type of pump
Principle
Approximate
pumping rate at
atmospheric
pressure
(litres per minute)
Water-operated Constricting a water jet
filter
reduces the pressure by
the Bernouilli effect.
Approximate
ultimate
pressure*
(mbar)
Comment
1
20
This figure can be bettered with a
well-designed pump. However,
water pressure is often too low to
achieve even this.
Hand pump,
Mitivac
A piston compresses air
from the vessel being
evacuated and forces it
out through a valve.
1-2
170
Pumping rate assumes roughly one
squeeze a second.
Hand pump,
Vacu-vin
A piston compresses air
from the vessel being
evacuated and forces it
out through a valve.
1-2
?
Only suitable for rough evacuation
of vessels with internal neck diameters of approximately 20 mm.
Electricallyoperated
diaphragm
A vibrating diaphragm
compresses air from the
vessel and forces it out
through a valve.
5 - 20
500 - 25
Electricallyoperated rotary
A vane projecting from a
cylinder rotating eccentrically compresses air and
forces it out through a
valve. See the diagram in
the Handbook, section
12.20.3.
40 - 50
Single stage:
10-1 - 10-2
Oil-diffusion
*
Double stage:
10-2 - 10-3
(Double-stage
rotary pumps
consist of two
single-stage
pumps in
series.)
10-4
-
Molecules of gas are
swept away by jets of oil
vapour.
High ultimate pressure and low flow
rate but maintenance-free. Suitable
for filtration. While less effective for
physics experiments than a rotary
pump, it can be used particularly if
its ultimate pressure is near 25 mbar.
Can also be used to produce
pressures above atmospheric.
Low ultimate pressure and high
flow rate and so best for physics
experiments.
Most rotary pumps are fitted with a
ballast facility. See section 4.
The exhaust must be connected to
a rotary pump. It has a high
displacement rate even at low
pressures and so will reach low
pressures despite minor leaks.
This is absolute pressure, ie, above zero pressure or a complete vacuum. Eg, an absolute pressure of 170 mbar is approximately 830 mbar below atmospheric pressure (which is approximately 1000 mbar).
Table 1.1
Conversions of units
Quantity
from:
to:
multiply by:
Flow rate
m3
(cubic metres per hour)
Pressure
torr
(mm of mercury)
mbar
(millibar)
1.33
bar
(atmospheric pressure is approx 1 bar)
kPa
(kilopascal - a pascal is a kilonewton per square metre)
100
hr-1 l
(litres per minute)
2
min-1 16.67
Table 2
Experiments, with pressures and pumps required
Use
Pressure*
needed
(mbar)
Pump
required
Comment
Physics experiments
Collapsing
can
970
Any.
Slower and less dramatic if a filter pump or manual pump is used.
Or, by displacing air in the can with steam from water boiled in it,
removing from the source of heat and sealing.
Magdeburg
hemispheres
800
Any.
Assuming that the internal diameter of the spheres is approximately 60 mm or less. See † below.
Guinea and feather
200
Filter, diaphragm or
rotary.
See † below.
Boiling under
reduced press ure
200
Filter, diaphragm or
rotary with ballast.
If a rotary pump must be used, it should be a model fitted with a
ballast or it should subsequently be purged of water vapour. Boiling under reduced pressure can be demonstrated without a pump,
by boiling water in a round-bottomed flask, removing the source of
heat, sealing the flask and cooling it. However, it is not so clear
what is happening.
Expansion of a
balloon
70
Filter, diaphragm or
rotary.
See † below.
Bromine
diffusion
30
Filter, diaphragm or
rotary.
See † below. Bromine is CORROSIVE. See Hazcards.
Sound of a bell
30
Filter, diaphragm or
rotary.
See † below.
Columns of mercury
lifted by atmosphere
10
Rotary.
These experiments are convincing only if pressures of a few
millibars can be obtained.
CARE with mercury: see Handbook, section 12.20.1.
Discharge through
gases
Cathode rays
Rotary.
Ideally cathode rays could be obtained with a double-stage rotary
pump. However, leaks and contamination make an oil-diffusion
pump necessary in practice.
10-3
Diffusion, backed
with rotary.
-
200
Filter, diaphragm,
See ‘Boiling under reduced pressure’ just above.
rotary with ballast or
hand pump.
7 x 10-1
Chemistry procedures
Vacuum distillation,
evaporation to
dryness etc
*
This is absolute pressure; eg, to collapse a can the pressure inside should be reduced to approximately 970 mbar, that is
30 mbar below atmospheric pressure.
†
The success of these experiments with a diaphragm pump depends on the low pressure rating of the pump, the size of the
system being evacuated and the presence of leaks. A rotary pump is more reliable.
3
Table 3
Rotary, diaphragm and hand pumps compared
Type of pump Vacuum Flow
reached rate
Mass
Working life
Maintenance
Price
Comment
Rotary
Advantages
Low.
High.
Disadvantages
Long.
-
About
10 kg.
Simple
maintenance £400 - 600
needed regularly to avoid
contamination of the oil,
usually with water vapour.
See Handbook section
12.20.3.
-
2 – 5 kg.
Very little needed.
-
Diaphragm
Advantages
Disadvantages Not very Low.
low.
£120 - 250
Short but likely
to be adequate
with school use.
-
Filter pump
Advantages
Not
Long.
significant.
Very little needed.
£5 - 30
Disadvantages Not very Low.
low.
Requires good
water pressure.
Wastes water.
Hand pumps
Mitivac
Advantages
Not
Short.
significant.
Very little needed.
£30 - 55
Disadvantages Not very Very
low.
low.
-
Vacu-vin
Advantages
Not
Short.
significant.
None needed.
Disadvantages Not very Very
low.
low.
Around £7
Needs
two
hands just to
operate pump.
Which type to buy
If it can be afforded and given a minimum of care and maintenance, a rotary pump is
advised for physics experiments. For uses involving vapour, including water vapour,
passing through the pump, a diaphragm pump is suitable. However, it will not achieve
a low enough pressure for some physics experiments carried out in large vessels, eg, bell
jars; see Table 2. A hand pump can be used to evacuate small systems but these must be
well-designed to avoid leaks.
For pumps for vacuum filtration, see section 7.
4
4.
Rotary pumps
For further information on rotary pumps, see the Laboratory Handbook, section 12.20.
Features included in Table 4
Some require no explanation.
•
Number of stages A two-stage pump consists of two rotary pumps in series and
achieves a lower pressure. Such a pump is not required except for work on electric
discharges at low pressures for which a diffusion pump backed with a rotary
pump is better, although a very well-maintained two-stage rotary pump can be
used to show many of the phenomena.
•
With ballast/without ballast A ballast is the provision of a small flow of air
through a pump, even when the inlet is blocked or at low pressure. Properly used,
it will minimise the contamination of the pump oil during use and purge such
contamination before and after use. It can be shut off to achieve the lowest pressures, hence the two pressures quoted.
•
Oil charge The amount of vacuum pump oil required by the pump.
•
Oil-mist filter Vacuum pump oil has a very low vapour pressure, ie, it produces
very little vapour; otherwise it could not be used, as the oil vapour would fill the
vacuum the pump was trying to produce. However, the oil in a pump can be carried out in the exhausted air in the form of tiny droplets, ie, a mist, particularly
when the flow of air or other gas through the pump is high.
The Occupational Exposure Standard (OES) for pump oil is 5 mg m-3 but currently
under review. While this level is unlikely to be approached during the use of a
pump in a space as large as a school laboratory during normal demonstrations, if
used for long periods in a smaller room the pump should be fitted with an oil-mist
filter, used in a fume cupboard or its exhaust led to a fume cupboard or out of a
window.
Schools are advised to purchase pumps with proper oil-mist filters; oil-mist plugs
are less effective.
•
Prices These are for rough comparison. Before purchase, buyers should check
current prices and consider discounts, delivery costs and VAT if applicable; see
section 10, Table 7.
•
Anti-suck back Without such provision, oil will be sucked from inside the vacuum
pump back into the system, eg, a bell jar, unless the operator remembers to close
the system off and let air into the inlet of the pump. A few moments forgetfulness
can ruin a demonstration and require a tedious cleaning job.
In several pumps, anti-suck back provision will let air into the evacuated system
when the pump is switched off, which therefore needs to be shut off with a tap
first if the system is still to be kept evacuated.
•
Specify inlet Specialist vacuum pump companies, eg, Edwards, Javac, Leybold
and MSVS, supply pumps with a range of inlet fittings. It is prudent when ordering direct from such a company to specify ‘inlet to take pressure tubing 6 mm
internal diameter etc.’
•
Addresses Given in section 10.
5
Table 4
Rotary Pumps under £600
Manufacturer
Not known
Edwards
Javac
Javac
Javac
Leybold
Leybold
Name
Minilab
SM302
Speedivac 2
DSL40
ES2
ED2
TS3
TD3
Number of stages
1
1
1
1
2
1
2
Vacuum (mbar)
with ballast
without ballast
8 x 10-2
6
1.3 x 10-1
2 x 10-1
4 x 10-2
1
10-1
10-1
2 x 10-2
8 x 10-1
8 x 10-2
2 x 10-2
2 x 10-3
Pumping Rate
(l min-1)
50
45
40
33
33
50
50
Outlet oil-mist filter
Filter plug.
Fitted.
Optional
extra:
LF002 £32.
Optional
extra:
LF002 £32.
Optional
extra:
LF002 £32.
Filter plug.
Separate
filter extra.
Filter plug.
Separate
filter extra.
Anti-suck back
protection
Fitted.
Optional
extra.
Fitted.
Fitted.
Fitted.
Fitted.
Fitted.
Oil charge (ml)
300
500
500
500
400
220
220
Mass (kg)
8.7
12.5
10.5
9.5
10
9.5
10
Dimensions
w x d x h (mm)
277 x 152 x
243
367 x 147 x
204
357 x 130 x
215
357 x 130 x
215
357 x 130 x
215
277 x 152 x
195
277 x 152 x
195
PYB-580-011J
PYB-580-020Y
326/0800/02
£425.01
326/0800/04
£499.01
Supplier
Bewhay
Catalogue number
Price
A134519012
£600, including oil-mist
filter EMF3,
mains plug,
delivery.
Griffin & George
Catalogue number
Price
Philip Harris
Catalogue number
Price
£405
Includes oilmist filter.
Y46260/6
£623.42
Javac
Catalogue number
Price
DSL40
£470
Specify inlet
nozzle.
ES2
£345
Specify inlet
nozzle.
Merck
Catalogue number
Price
Sci & Chem Sup
Catalogue number
Price
Note
£472
Includes oilmist filter.
ED2
£399
Specify inlet
nozzle.
PY550.10
£470
NO
BALLAST
Special price
for schools.
Mention
CLEAPSS in
orders.
Oil-mist filter
from Sci &
Chem Sup
costs more
than from
Javac.
6
Less finished,
eg, unpainted, version of
DSL40.
Not made by Leybold but
imported by it. Although not
in its catalogue, Leybold will
sell these pumps direct,
although it prefers to sell
them through laboratory
suppliers.
Table 4
Rotary Pumps under £600 (continued)
Manufacturer
MSVS
Name
G-2
Catalogue number
MSVS
740-086-00
2G-2
MSVS
740-071-01
SM02
MSVS
740-076-00
DM02 740-078-00
Number of stages
1
2
1
2
Vacuum (mbar)
with ballast
without ballast
8 x 10-1
6 x 10-2
3 x 10-2
8 x 10-4
8 x 10-1
5 x 10-2
3 x 10-2
8 x 10-4
Pumping Rate (l min-1)
36
36
50
50
Outlet oil-mist filter
Fitted.
Fitted.
Fitted.
Fitted.
Anti-suck back protection
Fitted. See* below.
Fitted. See* below.
Fitted. See* below.
Fitted. See* below.
Oil charge (ml)
200
150
300
200
Mass (kg)
5.5
6
9.5
10
Dimensions: w x d x h (mm)
252 x 110 x 165
252 x 110 x 165
275 x 135 x 240
275 x 135 x 240
Supplier
Irwin-Desman
Catalogue number
Price
RA6044
£534
NB: see = below.
MSVS
Catalogue number
Price
740-086-00
£320.92
Specify inlet nozzle.
Notes
740-088-00
£380.79
Specify inlet nozzle.
740-076-00
£450.85
Specify inlet nozzle.
740-078-00
£525.85
Specify inlet nozzle.
*
The anti-suck back protection is a valve which could allow oil back after a period of 15
minutes +. A solenoid valve giving complete isolation costs approximately £50 more.
=
If supplied by Irwin-Desman, no oil-mist filter or anti-suck back protection will be fitted.
Which models to buy
Best value, including oil-mist filter, anti-suck back protection and delivery charges, is
the MSVS G-2, at about £340. Next, at around £400, are the Javac ES2 and the MSVS 2G2.
The Leybold TS3 from Griffin and George at £405 comes fourth.
Table 4.1
Suppliers of oil for rotary pumps
Company
Name of oil
Minimum quantity (l)
Price
Catalogue number
Duravac
Duravac 105
5
£10.55
105
Griffin & George
Pump oil
1
£6.50
PYB-584-010K
Philip Harris
Rotary pump oil
1
£12.06
Y46262/9
Irwin-Desman
Vacuum pump oil
5
£19
RB6044
Javac
Pump oil V100
5
£10
V100
Jencons
TW mineral oil
1
£40.30
520-031
Merck
Edwards Ultragrade 19
1
£8.06
326/0705/01
MSVS
Rotary Pump oil
1
£7.50
610-0-003-01
Sarose
Ultragrade 15
4
£16.80
PY417.63
Sci & Chem Supplies
Ultragrade 15
4
£22.85
PY417.63
Price differences reflect quality; for school use, a less expensive oil is adequate. There is no point in buying a large quantity of
oil unless the oil in a pump is replaced regularly. Where the minimum quantity is 1 litre, larger containers are usually available.
NB Delivery charges on a few litres of pump oil can increase the price considerably. Check.
7
5.
Diaphragm pumps
These are hardly considered in the CLEAPSS Laboratory Handbook as they were seldom
used in schools until recently. Now their price advantage, compactness and minimum
maintenance make them well worth considering.
Features included in Table 5
Most require no explanation.
•
Output pressure Diaphragm pumps can be used to provide pressures above
atmospheric pressure; ie, they can be used to inflate balloons etc.
•
Prices These are for rough comparison. Before purchase, buyers should check
current prices and consider discounts, delivery costs and VAT if applicable; see
section 10, Table 7.
•
Addresses Given in section 10.
Table 5
Diaphragm pumps with prices below £250
Manufacturer
Charles Austen
KNF Neuberger
Name
DYMAX 30
DA7C
CAPEX L2C
Econovac
N86KN.18
VP1HV
Vacuum (mbar)
540
410
300
200
100
25
Output pressure
(kPa)
75
120
200
130
240
-
Pumping rate
(l min-1)
5
14
6.5
18
6
5
Mass (kg)
2.75
2.75
3.75
5
?
2
Dimensions
w x d x h (mm)
205 x 140 x 120 205 x 140 x 120 230 x 180 x 160 230 x 145 x 140 205 x 180 x 110 185 x 145 x 175
Supplier
Astell
Catalogue number
Price
PNJ112
£232.95
Charles Austen
Catalogue number
Price
DYMAX 30
£155.75
Griffin & George
Catalogue number
Price
PXW-540-010B PXW-540-020V
£165
£202
Philip Harris
Catalogue number
Price
DA7C
£191.65
CAPEX L2C
£232.95
PXW-605-010X
£135
PXW-610-010X
£220
Y46180/8
£243.40
KNF Neuberger
Catalogue number
Price
Econovac
£134.50
Merck
Catalogue number
Price
326/0118/00
£164.96
Sarose
Catalogue number
Price
PX305
£150.48
326/0115/00
£246.61
Sci & Chem Sup
Catalogue number
Price
VP1HV
£215.25
326/0128/02
£189.49
PY510.10
£148.62
8
N86KN.18
£174.55
PY530.30
£220.63
Which models to buy
The KNF VP1HV achieves a pressure below other diaphragm pumps and so is more
effective for physics experiments. It will also produce a good filtration rate on four
Büchner flasks. If filtration is the only use anticipated, then a cheaper pump, eg, the
Econovac or DA7C, would be suitable.
6.
Hand pumps
6.1
The Nalgene Mitivac
Several companies sell various models of a small hand pump called the ‘Mitivac’ made
by Nalgene in the USA.
Features, including those in Table 6 (overleaf)
•
External vacuum release valve All models are fitted with this. If actuated, this will
let air back into the system.
•
Inlet nozzle This has a diameter suitable for PVC or rubber pressure tubing with
an internal diameter of 6 mm.
•
Vacuum gauge These pumps are sold with and without vacuum gauges. A gauge
can be useful in many cases, eg, for indicating the existence of leaks or for checking
that liquid is not being pulled through a filter paper too rapidly.
•
Displacement per stroke There are two sizes of pump, with displacements per
stroke of 15 cm3 or 36 cm3. Assuming the pump can be squeezed and released once
a second, flow rates of approximately 1 litre min-1 and 2 litre min-1 can be obtained.
This is a low rate and so hand pumps are able only to evacuate small leak-free
systems.
•
Repairable/not repairable Models of both types are available. Repairable pumps
cost more but can be taken apart for the replacement of springs, gaskets etc from a
kit sold separately.
•
Vacuum claimed 170 mbar. This is comparable with that of the diaphragm pumps
listed which have a range of 480 - 25 mbar.
•
Material Most models are of white PVC but one, which is harder wearing, is made
of zinc alloy.
Which models to buy
Unless the system to be evacuated is very small, the 36 cm3 per stroke size is preferable.
A fitted gauge is useful. There is insufficient experience of the use of these pumps to
decide whether it is sensible to pay extra for repairable or for alloy versions.
6.2
Vacu-vin pump
A Vacu-vin pump is designed to extract the air from a partially empty wine bottle, to
reduce oxidation of the remaining wine. A set consists of two parts, a small plastic
pump and some neoprene stoppers, and costs about £7 at Boots, wine merchants etc. It
can be used for vacuum filtration; see section 7, with the diagram on page 11. The
neoprene stoppers are designed for wine bottles and so will fit only in Büchner flasks or
side-arm test tubes with internal diameters 20 mm or slightly less.
9
Table 6
Nalgene Mitivac hand pumps: models supplied
6130 -0010
Nalgene
Catalogue
number
Material
6130 -0020
6131-0010
6131-0020
6132-0010
6132-0020
6133
PVC
PVC
PVC
zinc alloy
Vacuum
gauge fitted?
4
6
4
4
Repairable? =
6
6
4
4
Displacement
per stroke
(cm3)
15
36
15
36
15
36
15
Suppliers
Fisher
Cat number
Price
PXW-975-010K PXW-975-020H PXW-975-100J
£51.04
£55.00
£36.48
PXW-975110G
£45.19
G&G
Cat number
Price
Philip Harris
Cat number
Price
Y46100/6
£65.23
Jencons
Cat number
Price
521-003
£41.30
521-001
£47.50
Merck
Cat number
Price
326/0026/10
£51.04
326/0026/20
£55.00
Sci & Chem
Supplies
Cat number
Price
PX205.10
£50.00
PX205.20
£55.00
Techmate
Cat number
Price*
6130-0010
£43.38
6130-0020
£46.75
521-004
£31.50
521-002
£37.25
6131-0010
£31.00
6131-0020
£38.41
PXW-978-010P PXW-978£53.63
020M
£57.73
PXW-978-100X
£67.75
PXW-978-010P PXW-978£46.10
020M
£49.65
PXW-978-100X
£56.25
6132-0010
£45.59
6133
£57.59
6132-0020
£49.07
= Repair kits are available for the repairable pumps. These contain silicone lubricating oil, springs,
gaskets, screws etc; also a diagram of the pump.
*
7.
A 15% discount for schools has been subtracted.
Vacuum for filtration
The disadvantages of water-powered filter pumps were discussed in section 2.
Alternatives are:
For a single Büchner flask: A Mitivac, a Vacu-vin, a diaphragm pump or a rotary
pump.
For three to five Büchner flasks: A diaphragm pump or a rotary pump.
(A rotary pump employed to achieve low vacuum for other experiments should not be
used as its oil will become contaminated with water, unless care is taken.)
10
Tests of filtration with these pumps, using Büchner funnels* taking 40 mm and 90 mm
diameter papers, showed that all these alternatives to water-powered filter pumps were
successful. However, there was a danger with all methods that filtration could be too
rapid, with too much of certain suspensions pulled through the filter. The danger can be
reduced by using two papers.
•
Mitivac evacuating one Büchner flask. The pump can be operated easily in the left
hand, leaving the right hand free to wet the filter paper with a wash bottle and
pour the suspension into the funnel. The model used was fitted with a pressure
gauge which made it easy to adjust the rate of flow through the filter.
•
Vacu-vin evacuating one Büchner flask. This required two operators, one to hold the
side-arm test tube and operate the pump, the other to wet the filter paper with a
wash bottle and pour the suspension into the funnel. The rate of flow through the
filter can be adjusted by the number of strokes of the pump.
The arrangement is shown in the diagram; the thick-walled side-arm test tube
must have an internal diameter less than 20 mm, eg, 19 mm, for the stopper to fit.
Passing the pressure tubing through a slightly-tightened clamp in a stand prevents
over-vigorous pumping from knocking the Büchner flask over. It is important to
keep the Vacu-vin stopper wet to produce good seals, including that between the
pump and the stopper.
Arrangement for one Büchner flask connected to a Vacu-vin pump
Clamp to steady
pressure tubing
Pressure tubing to
Büchner flask
*
Vacu-vin
stopper
Side-arm
test tube
with
internal
diameter
20 mm or
slightly
less
One batch of Büchner funnels purchased by CLEAPSS caused problems: the diameter was not standard and so
filter papers had to be cut to fit. In addition, perforations were too large, causing holes to be sucked through the
papers during use. Schools sent similar funnels should return them without hesitation.
11
•
Diaphragm pump evacuating up to four Büchner flasks. A tube with an adjustable
‘bleed’, ie, a controlled leak of air, can be used to prevent too rapid filtering; see
the diagram. The copper wire makes the bleed more responsive to the turning of
the screw on the clip. In the arrangement for several flasks, a tube should be sealed
with a Mohr or Hoffmann clip if not connected to a flask.
(A rotary pump with a flow rate of 50 litre min-1 can be expected to perform at
about twice the rate of a diaphragm pump.)
'Bleeder' tube
Hoffmann
clip
copper wire, approx
1/2 mm
pressure tubing
Arrangement for one Büchner flask connected to a diaphragm
Bleeder valve
Hoffmann
clip
outlet
Diaphragm
pump
plastic Yconnector
to mains
socket
inlet
to Büchner
flask
Arrangement for several Büchner flasks connected to a diaphragm
Bleeder valve
outlet
Hoffmann
clip
to Büchner
flasks
Diaphragm
pump
plastic Yconnector
inlet
plastic Yconnector
plastic Yconnector
Mohr
clip
12
to mains
socket
8.
Repair companies
Two companies which schools have found useful are:
•
Applied Vacuum Engineering Ltd,
•
Coleman Engineering.
Before summoning a company to service a vacuum pump, a school should telephone to
explore the likely cost; the call-out charge for specialist work can be high. It may also be
necessary to ensure that work is not carried out to standards which are unnecessary for
schools.
9.
Accessories
Several school suppliers provide equipment for carrying out demonstrations involving
vacuum. It is not intended to list these but merely to draw attention to two items which
might otherwise escape notice. The first is a series of small polycarbonate or
polyetherimide vacuum chambers of different sizes with matching vacuum plates sold
by Techmate (5305). These are smaller but safer than some glass bell jars; prices start at
£105 for two. Unfortunately, while transparent, the chambers are tinted which will
slightly reduce visibility. MSVS supplies a range of apparatus for vacuum experiments.
This includes: base plate and bell jar with pressure gauge, £255.75; Magdeburg
hemispheres £117; bell and electric connections £106; guinea and feather tube £217 etc.
Further details are available from MSVS; however, schools are likely to find these items
expensive.
10.
Discounts, charges and addresses
Table 7
Discounts, delivery charges etc
Company
Discounts
Delivery charges
Astell
-
Below £200, £9.95; above £200, zero.
Charles Austen
-
At cost.
Bewhay (for Edwards)
£600 for the Speedivac 2 is a
special school price.
Included.
Duravac
-
£8.
Fisher
-
None.
Griffin & George
-
None.
Philip Harris
Under £100
Over £100
Over £2000
Irwin-Desman
-
None for CLEAPSS members.
Javac
-
At cost, typically £15 for one pump.
Jencons
-
At cost.
None
10%
Negotiable.
None.
KNF Neuberger
-
At cost.
Merck
-
Depends on agent. Likely to be at cost.
MSVS
-
£16 standard charge.
Sarose
-
£7.90 up to 10 kg.
Scientific & Chemical
Supplies
Discounts on some items but
not vacuum pumps.
Below £25, £5 handling charge; £25 - £200, charge variable up
to £20; above £200, free.
Techmate
15% for schools, deducted
Freight charges at cost, plus small packaging fee.
from prices quoted in Table 6.
13
Addresses
Applied Vacuum Engineering Ltd
Unit 8, Mead Court
Thornbury
Bristol BS12 2UW
Tel: 01454 413561
Fax: 01454 411700
Philip Harris Education
Lynn Lane
Shenstone
Lichfield WS14 0EE
Tel: 01543 480077
Fax: 01543 480068
Astell Scientific Ltd
Powerscroft Road
Sidcup DA14 5DT
Tel: 0181 300 4311
Fax: 0181 300 2247
Irwin-Desman Ltd
Eurocrown House
23 Grafton Road
Croydon CR9 3AZ
Tel: 0181 686 6441
Fax: 0181 681 8429
Charles Austen Pumps Ltd
Royston Road
Byfleet
West Byfleet KT14 7NY
Tel: 01932 355277
Fax: 01932 351285
Javac (UK) Ltd
Unit 6, Drake Court
Britannia Park
Middlesborough TS2 1RS
Tel: 01642 232880
Fax: 01642 232870
Coleman Engineering
20 Brittania Estate
Leagrave Road
Luton LU4 8HZ
Tel: 01582 452962
Fax: 01582 484518
Jencons (Scientific) Ltd
Cherrycourt Way Industrial Estate
Stanbridge Road
Leighton Buzzard LU7 8UA
Tel: 01525 372010
Fax: 01525 379547
BDH; see Merck Ltd
KNF Neuberger (UK) Ltd
Industrial Estate
Station Lane
Witney OX8 6FA
Tel: 01993 778373
Fax: 01993 775148
Bewhay Vacuum & Technical Ltd
High Canons, Well End
Boreham Wood
WD6 5PL
Tel: 0181 207 5044
Fax: 0181 207 4556
(Retailers for Edwards High Vacuum)
Leybold
Waterside Way
Plough Lane
London SW17 7AB
Tel: 0181 971 7000
Fax: 0181 971 7001
Duravac Products Ltd
Unit 170, John Wilson Business Park
Whitstable CT5 3RA
Tel: 01227 770828
Fax: 01227 770878
Merck Ltd (formerly BDH)
Merck House
Poole BH15 1TD
Tel: 01202 669700
Fax: 01202 665599
(Contact for details of local dealers)
Edwards High Vacuum International:
see Bewhay
Fisher Science (UK)
Bishop Meadow Road
Loughborough LE11 0RG
Tel: 01509 231166
Fax: 01509 231893
MSVS Ltd
Unit 6 Old Station Industrial Park
Lower Farringdon
Alton GU34 3DP
Tel: 01420 587244
Fax: 01420 587241
Griffin & George
Bishop Meadow Road
Loughborough LE11 0RG
Tel: 01509 233344
Fax: 01509 231893
14
Nalgene: see Techmate
Sarose Scientific & Instruments
Units 33-34, Sheraton Business Centre
Wadsworth Road
Perivale
Greenford UB6 7JB
Tel: 0181 997 5941
Fax: 0181 997 7700
Scientific & Chemical Supplies
Carlton House
Livingstone Road
Bilston WV14 0QZ
Tel: 01902 402402
Fax: 01902 402343
Techmate Ltd
10 Brideturn Avenue
Old Wolverton
Milton Keynes MK12 5QL
Tel: 01908 322222
Fax: 01908 319941
(Importer for Nalgene)
15