3B Scientific Pressure Balance User Manual

Page 4

..... Description, technical data

Two precision-made glass syringes [

] of differing

volume are attached to an acrylic carrier plate

on top

of an anodised aluminium stand rod

. Each of the

plungers has a tray

for holding weights

. The sy-

ringes are linked by a connecting hose

so that they

form a closed system

. An air inlet

allows air to be

drawn into the system

. A safety cord prevents the small

plunger flying out of the cylinder

. A rod

is included on

the base plate

upon which disc weights can be stacked

when not in use

Volume of syringes:

10 ml and 50 ml

Ratio of plunger
diameters:

10:3 (

∅ 26.9 mm : 14.7 mm)

Ratio of plunger masses
with tray:

10:3

Number of weights:

Mass of weights:

40 g each (approx

Base plate dimensions:

140 mm x 100 mm

Total weight:

.2 kg

..... Operation

• Preparation: open the air inlet, pull out the large cyl-

inder to about the 20-30 ml mark then close the inlet
again

• Experiment procedure: first lay a weight onto the

small plunger

. Next lay weights one by one on top of

the large plunger

. When the fourth weight is laid on,

the plunger starts to descend

• Thus when the weight ratio is about 1 : 3.5 ± 0.5

weights, the system is in equilibrium

. This ratio is

confirmed by placing weights in the ratio of 2 : 7 (if
the plungers are very clean and weights precisely cen-
tered, the large plunger may start to descend)

. Equi-

librium is also apparent for a weight ratio of 3 : 10

• During the course of an experiment, air gradually

seeps out since syringes that were entirely airtight
would not move at all

. It may be necessary to let in

more air

..... Storage and cleaning

• For the equipment to function perfectly, it is essen-

tial that the plungers and cylinders are free of any
grease or dust

. Even fingerprints can affect the func-

tionality adversely

. The equipment can be cleaned

using methylated spirits (caution: flammable!)

. If the

safety cord is removed to facilitate cleaning, it can be
replaced by any suitable strong nylon cord (e

.g. but-

tonhole thread)

• The equipment should be stored in a dry, dust-free

location

3B Scientific GmbH • Rudorffweg 8 • 21031 Hamburg • Germany • www.3bscientific.com • Technical amendments are possible