3B Scientific Pressure Balance User Manual

Page 2

.....

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 (

∅

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

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

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