The document discusses the components and functioning of an anaesthesia work station's high pressure system. It describes the key components including gas cylinders, hanger yokes, cylinder pressure indicators, and pressure regulators. Gas cylinders contain medical gases at high pressure and have valves, handles, pressure relief devices, and markings. Hanger yokes orient and secure cylinders, providing a gas-tight seal. Cylinder pressure indicators display the pressure level in cylinders. Pressure regulators reduce the high cylinder pressure to a lower, constant pressure suitable for use in the anaesthesia machine.

1. SRI SIDDHARTHA MEDICAL COLLEGE
High Pressure System
Chairperson : Dr.S.B.Gangadhar
Moderator : Dr. C.N. Ramesh
Presenter : Dr. Daber Pareed

2. Introduction
• Anaesthesia work station is a device which delivers a precisely known
but variable gas mixture, including anaesthetizing and life sustaining
gases.

3. History
• The original concept of Boyles machine was invented by the british
anaesthetist H.E.G Boyle in 1917
• 1920 – A vaporizing bottle is incorporated with the machine.
• 1926- A 2nd vaporizing bottle and by pass controls are incorporated.
• 1930- A plunger device is added to the vaporizing bottle.
• 1933 – A dry bobbin type of flowmeter is introduced.
• 1937 – Rotameters displayed dry bobbin typle of flowmeters

4. Anaesthesia Work Station
• Integrates most of the components necessary for administration of
anesthesia into single unit.
• Standard guidelines have been given to manufacturers for minimum
performance, design, characteristics and safety requirements of
machine.

5. During the past two decades, the progression of anaesthesia machine
standards has been as follows-
• 1979 – American National standards Institute.
• 1988 – American society for Testing and Materials,
• 1994 – ASTM F1161-94 ( reapproved in 1994 and discontinued in 2000)
• 2005 – International Eletrical commission.
• 2005 – ASTM (reapproved) F1850
• European Standard is EN740
https://www.astm.org/Standards/F1850.htm

7. Types of Anaesthesia Machine
• INTERMITTENT – Gas flows only during inspiration.
Eg: Entonox apparatus, Mackessons apparatus
• CONTINOUS – Gas flows both during inspiration & Expiration.
Eg. Boyles Machine

8. System Components
ELETRICAL PNEUMATIC
1. MASTER SWITCH
2. POWER FAILURE
INDICATOR
3. RESERVE INDICATOR
4. ELETRICAL OUTLET
5. CIRCUIT BREAKERS
6. DATA COMMUNICATION
PORTS
1. HIGH PRESSURE SYSTEM
2. INTERMEDIATE PRESSURE
SYSTEM
3. LOW PRESSURE SYSTEM

10. Components of Pressure System

12. Medical Gas Cylinders – Components
Body
• Previously most of the gas cylinders are constructed of steel, with
various alloys added.
• In recent years, it have moved away from traditional steel cylinders
towards steel carbon fiber cylinders. These can hold more gas than
the older steel counterparts
• These are especially useful in MRI environment.
• Cylinders have a marking “3AA” are manufactured using steel and
“3ALM” or “3AL” indicated that cylinder is made from aluminium.

13. Valve
• Cylinders are filled and discharged through a valve attached to the
neck.
• Made up of Bronze or Brass.
PORT- it is the point where the gas exits.
STEM- each valve contains a stem or shaft, that is rotated during valve
opening or closing.

14. VALVE
PACKED VALVE –
• most cylinder valves are of the packed type.
• The Stem is sealed by resilient packing such as Teflon, which prevents
leaks around the threads.
DIAPHRAGM VALVE –
• In a diaphragm valve closure between the cylinder interior and the
atmosphere is accomplished by using a seal, usually metal to metal,
and a bonnet nut that clamps one or more circular discs in place.

15. HANDLE OR HANDWHEEL
• It is used to open or close a cylinder valve.
• This causes the stem to turn.
• Handles come in variety of shapes.
• The hazards associated with the handle is
that a person unacquainted with cylinders
could loosen the packing nut under the
mistaken impression that he or she was
opening the valve.

16. PRESSURE RELIEF DEVICES
• Every cylinder is fitted with a pressure relief (safety
relief, safety) device whose purpose is to vent the
cylinder’s contents to atmosphere, if the pressure of
the enclosed gas increases to a dangerous level.
RUPTURE DISC:
• The rupture disc is non-reclosing device with a disc
held against an orifice.
• When the predetermined pressure is reached, the disc
ruptures and allows the cylinder contents to be
discharged.
• It protects against excess pressure as a result of high
temperature or overfilling.

17. FUSIBLE PLUG
• The fusible plug is thermally operated, non-reclosing pressure-relief device with
plug held against the discharge channel.
• It offers protection from excessive pressure caused by a high temperature but not
from overfilling.
• The yield temp; is the temp; at which the
fusible material becomes sufficiently soft to extrude
from its holder.
So, that cylinder contents gets discharged.
COMBINATION RUPTURE DISC/FUSIBLE PLUG
• It can be used to prevent bursting at a predetermined pressure unless the
temperature is high enough to cause the fusible material to yield.
Pressure Relief
Device

18. PRESSURE RELIEF VALVE
• It is a spring-loaded device designed to reclose and prevent cylinder
contents from being discharged after a normal pressure has been
restored.
CONICAL DEPRESSION
• It is present on the small cylinders above the safety relief device, and
it receives the retaining screw of the yoke.

19. SIZES OF GAS CYLINDERS
• Classified by using a letter code, with A being the smallest.
• Size E is the cylinder most commonly used on anesthesia machine and
for patient transport and resuscitation.
• Size D cylinders are used for limited supplies of gases where size and
weight considerations are important.

21. CONTENTS AND PRESSURE
• In a cylinder containing non-liquefied gas, the pressure declines
steadily as the contents are withdrawn. Therefore, the pressure can
be used to measure the cylinder contents.
• In a cylinder containing a liquefied gas, the pressure depends on the
vapour pressure of the liquid and is not an indication of the amount
of gas remaining in the cylinder as long as the contents are partly in
the liquid phase.
• Weight can be used to determine the amount of liquid in these
cylinders.

22. Testing
• A cylinder must be inspected and tested at least every 5 years or with a
special permit ,upto 10 years.
• The test date (month and year) must be permanently stamped on the
cylinder.
• Each cylinder must pass an internal and external visual check for corrosion
and evidence of physical impact or distortion.

23. Filling
• The pressure in a filled cylinder at 70 degree F may not exceed the
service pressure marked on the cylinder except for some nonliquified,
non inflammable gases.
• For the gases other than nitrous oxide and carbon dioxide, the
pressure in the cylinder is 130degree F, may not exceed 1.25 times
the maximum permitted filling pressure at 70degree F

24. Markings
• They are permanently stamped, usually on to the
shoulder of the cylinder.
• The markings are for eg:
DOT-3A2015
8642
XYZ
JCN
o DOT specification is 3A, the service pressure is 2015psig
at 70degree F
o 8642 – Serial number
o XYZ- Manufacturer
o JCN- Owners Symbol

25. Labelling
• Each cylinder must bear the label
• It has diamond shaped figure denoting the hazard class of the
contained gas and a white panel with the name of the contained gas
to the left

26. Tags
• A typical tag has 3 sections labelled- FULL, IN USE & EMPTY
• When a cylinder is put into service, the FULL portion of the tag
should be detached.
• When the cylinder is empty, the IN USE portion should be
removed, leaving the EMPTY label.

27. Summary of Gas Cylinders

28. Components of High pressure System- Hanger Yoke
The Hanger yoke orients and supports the cylinder, provides a gas tight seal and ensures a
unidirectional gas flow.
The workstation standard requires that there be at least one yoke for oxygen and nitrous oxide.
Parts:
1. Body: Principle framework of yoke.
• Threaded into frame of machine, supports cylinder.
• It Provides support to the cylinder
• On the swinging gate, type of yoke, distal part is hinged.
• Hinged part can be swung side

29. 2. Retaning Screw
• The retaining screw is threaded into the distal end of the yoke.
• Tightening the screw passes the cylinder valve outlet against the
washer and nipple so that the gas-tight seal is achieved.
3. Nipple-
• The nipple is part of the yoke through which gas enters the
machine.
• It projects from the yoke and fits into the port on the cylinder
valve.
• If the nipple is damaged, it may be impossible to obtain a tight
seal with the cylinder valve.

30. 4. Index Pins
• The pin index system are below the nipple.
• The holes into which the pins are fitted must be of a specific depth.
5. Washer
• A washer is placed around the nipple to produce a seal between the
cylinder valve and the yoke.
• A washer is usually supplied with each full cylinder
• Bodok seal is made of non combustible material, has a metal
periphery to make it long lasting
• Should be <2.4mm thick
• Only one seal allowed between the valve and yoke.

31. 6. Filter- (100 µm maximum)
• The anaesthesia work station standard requires that a filter be
installed between the cylinder and pressure regulator to prevent
particulate matter from entering the machine.
7. Check Valve Assembly-
• It allows gas from cylinder to enter machine but prevents gas
from exiting machine when yoke has no cylinder.
 Allows replacement of cylinders without losing gas
 Prevents transfer of gas from a cylinder with high pressure to one with
low pressure if connected to double yoke and turned on
simultaneously.
 A yoke should not never be left vacant.
 After tightening a cylinder to yoke should look for leaks
 After cylinder is attached valve should be closed.

32. • A typical check valve consist of plunger that slides away from the side
where the pressure is greater.
• When the cylinder pressure exceeds the pressure on the machine
side, the plunger is pushed to the right and gas passes around it and
into the machine.
• When the machine pressure exceeds the cylinder pressure, the
plunger moves to the left, blocking the gas flow.

33. Safety device in yoke
• Woods alloy- fusible plug of bismuth, lead, cadmium melts at 150-170
degree F, prevents explosion
• Copper frangible disc- ruptures at very high pressure.

34. Limitations of Check Valve assembly
• The check valves are not designed to act as permanent seals for
empty yokes.
• Small amounts of gases can escape if the yoke is empty or an empty
cylinder (or cylinder with low pressure) and valve open is present in
the yoke.

35. In order to minimize such losses –
• Yokes should not be left vacant for extended periods.
• An empty cylinder should be replaced as soon as possible , if not
then,
• An yoke plug can be used to prevent gas leak
Or
• An empty cylinder can be left behind after closing the valve.

36. • It is important that cylinder valves and yokes not be contaminated
with oil or grease, because this could present a fire hazard.
• Before a cylinder is mounted in place, the yoke should be checked to
make certain that the two Pin Index safety pins are present.
• A missing pin could allow the safety system to be bypassed.

37. Non Interchangeable safety system
PIN INDEX SAFETY SYSTEM
• It is a safety mechanism so that one cylinder cannot be fitted at the
others position.
• It consists of holes on the cylinder valve and 2 pins on the yoke
positioned to fit into these holes.
• The port will seal only with proper alignment of Pins and Holes
• Pins are 4mm diameter, 6mm long, except Pin 7 which is slightly
thicker.

39. Limitations of Pin Index system
• A wrong cylinder can be placed in the yoke, if
 2 washers are placed.
Pins on the yoke are broken
Holes in the cylinder valve are two deep

41. Cylinder Pressure Indicator (Bourdon Pressure Gauge)

42. Bourdon Pressure Gauge
• It displays the cylinder pressure for each gas supplied by cylinders.
• The indicator may be located near the cylinders or on a panel on the
front of the machine.
• Hollow metal tube of copper alloy, bent into a curve, sealed and
linked to a clock – like mechanism.
• Other end is connected to the gas source.

43. • Increase in gas pressure inside the tube causes it to
straighten.
• As the pressure falls, the tube resumes its curved
shape.
• These motions are transmitted to an indicator which
moves on a calibrated scale through clock like
mechanism.
• Gauages are required to be calibrated in kilopascals
(kPa)

44. Safety features in cylinder Pressure Indicator
• Gauge is usually color coded.
• Name and symbol of gas are written over dial.
• If bourdon tube ruptures gas is vented from back side.
• Gauges are angled and placed in such a way that it can be easily read by
anaesthetist.
• Instructions like “use no oil’’ “open the valve slowly’’ are written on the
gauge.

45. Electronic Cylinder Pressure Indicator
• Light emitting diodes(LED’S)in electronic pressure gauge indicate-
Cylinder Valve is close – Dark Color
Cylinder Valve is Open-
Pressure adequate – Green
Pressure inadequate – Red

46. Pressure Regulators
• The pressure in cylinder varies. To maintain constant flow with
changing supply pressure, the anaesthesia machine is fitted with
pressure regulators
• A pressure regulator reduces the high and variable pressure found in
a cylinder to a lower, more constant pressure suitable for use in
anaesthesia machine (40-45 Psig)

47. Physical Principle
A large pressure acting over a small area is balanced by a small pressure
over a larger area
SAFETY FEATURES!!
• Pressure regulators have safety relief valves
• If due to any reason there is build up of pressure in pressure regulator
then the safety valve blow off at a set pressure of 525 k pa(70psi)