INTERMEDIATE PRESSURE SYSTEM

1. INTERMEDIATE
PRESSURE SYSTEM
PRESENTER : DR. MOHIT JAGGA
MODERATOR : DR. PINU

2. The Intermediate Pressure System
Receives Gases From The Pressure
Regulator Or The Pipeline Inlet To The
Flow Control Valve Of The Anesthesia
Machine

3. Intermediate-pressure system

4. COMPONENTS
• Pneumatic Part Of The Master Switch
• Pipeline Inlet Connections
• Pipeline Pressure Indicators
• Piping
• Gas Power Outlet
• Oxygen Pressure Failure Devices
• Oxygen Flush
• Second Stage Pressure Regulators
• Flow Control Valves

5. PNEUMATIC PART OF MASTER SWITCH
• Located In The Intermediate Pressure System
Downstream Of Inlets For Cylinder And Pipeline
Supplies.
• The Oxygen Flush Is Usually Independent Of This Switch.
• Master Switch May Be Totally Electronic That When
Activated Controls The Various Pneumatic Components
Of The Anesthesia Machine.

6. PIPELINE INLET CONNECTION
• Pipeline Inlet Connection Is The Entry
Point For Gases From The Pipelines
• Mandatory N2O And O2, Usually Have
Air And Suction Too
• Inlets Are Non-interchangeable Due
To Specific Threading As Per The
Diameter Index Safety System (DISS)
• Unidirectional Valve To Prevent
Reversed Gas Flow
• Filter With A Pore Size Of 100 µm

7. DIAMETER-INDEXED SAFETY SYSTEM
• The DISS, Which Was Developed To Provide
Non-interchangeable Threaded
Connections For Medical Gas Pipelines,
Consists Of :
• Body
• Nipple
• Nut Combination
• There Are Two Concentric And Specific Bores In The Body And Two
Concentric And Specific Shoulders On The Nipple.
• The Small Bore Mates The Small Shoulder And The Larger Bore Mates
The Large Shoulder To Achieve Non-interchangeability Between Different
Connections.

8. PIPELINE PRESSURE INDICATOR
• Present On Panel On Front Of Machine And May Be Color Coded
• On Some Newer Electronic Machines, LEDS Indicate Pipeline Pressure
• The Workstation Standard Requires That Indicator Be On The Pipeline Side Of The Check
Valve In The Pipeline Inlet
• If The Indicator Is On The Pipeline Side Of The Check Valve, It Will Monitor Pipeline Pressure
Only
• If The Indicator Were On The Machine Side Of The Check Valve, It Would Not Give A True
Indication Of The Pipeline Supply Pressure Unless The Cylinder Valves Were Closed
• Pressure Should Be Between 50 And 55 Psig.

9. PIPING
• Must Be Able To Withstand Four Times The Intended
Service Pressure Without Rupturing
• Anesthesia Workstation Standard Specifies That Leaks
Between The Pipeline Inlet Or Cylinder Pressure Reducing
System And The Flow Control Valve Not Exceed 25
ml/Minute
• If Yoke And Pressure Reducing System Are Included, The
Leakage May Not Exceed 150 Ml/Minute

10. GAS POWER OUTLET
• May Serve As The Source
Of Driving Gas For The
Anesthesia Ventilator Or
To Supply Gas For A Jet
Ventilator

11. OXYGEN FAILURE SAFETY DEVICE
• Whenever The Oxygen
Supply Pressure Is
Reduced Below The
Manufacturer-specified
Minimum, The Delivered
Oxygen Concentration
Shall Not Decrease Below
19% At The Common Gas
Outlet

12. OXYGEN FAILURE CUT OFF VALVES (FAIL-SAFE)
• A Fail-safe Valve Is Present In The Gas Line Supplying
Each Of The Flowmeters Except O2
• This Valve Is Controlled By The O2 Supply Pressure And
Shuts Off Or Proportionately Decreases The Supply
Pressure Of All Other Gasses As The O2 Supply Pressure
Decreases.
• 2 Kinds Of Fail-safe Valves
• Pressure Sensor Shut-off Valve (Ohmeda)
• Oxygen Failure Protection Device (Drager)

13. Intermediate-pressure system

14. PRESSURE SENSOR SHUT OFF VALVE (OHMEDA)
• The Valve Is Threshold In Nature And It Is Either Open Or Closed
• Oxygen Supply Pressure Opens The Valve, And The Valve Return Spring Closes The
Valve
• Nitrous Oxide Pressure-sensor Shut-off Valve Has A Threshold Pressure Of 20 Psig
• Oxygen Supply Pressure Greater Than 20 Psig Is Exerted On The Mobile Diaphragm
• This Pressure Moves The Piston And Pin Upward, And The Valve Opens.
• Oxygen Supply Pressure Is Less Than 20 Psig, And The Force Of The Valve Return
Spring Completely Closes The Valve
• Nitrous Oxide Flow Stops At The Closed Fail-safe Valve, And It Does Not Advance
To The Nitrous Oxide Flow Control Valve

16. OXYGEN FAILURE PROTECTION DEVICE (DRAGER)
• OFPD Interfaces The Oxygen Pressure With That Of Other Gases.
• Based On Proportioning Principle.
• Pressures Of All Gases Controlled By OFPD Decrease Proportionally
With The Oxygen Pressure.
• Consists Of Seat-nozzle Assembly Connected To Spring-loaded
Piston.
• There Is A Continuum Of Intermediate Configurations Between The
Extremes Of Oxygen Supply Pressure.
• These Intermediate Valve Configurations Are Responsible For The
Proportional Nature Of The OFPD

18. The oxygen supply pressure is 50 psig on left panel, pushes the
piston upward, forcing the nozzle away from the valve seat.
• Nitrous oxide advance toward the flow control valve at 50
psig.
• The oxygen pressure in the right panel is zero psig.
• The spring is expanded and forces the nozzle against the seat,
preventing flow through the device.
• Finally, the center panel shows an intermediate oxygen
pressure of 25 psig.
• The force of the spring partially closes the valve.
• The nitrous oxide pressure delivered to the flow control valve
is 25 psig

19. OXYGEN SUPPLY FAILURE ALARM
• Whenever The Oxygen Supply Pressure Falls Below A Manufacturer-specified
Threshold ,Usually 37-35Psig , A Priority Alarm Shall Be Activated Within 5 Sec.
• They Aid In Preventing Hypoxia Caused By Problems Occurring Upstream In The
Machine Circuit.
• These Devices Do Not Offer Total Protection Against A Hypoxic Mixture Being
Delivered, Because They Do Not Prevent Anesthetic Gas From Flowing If There
Is No Flow Of Oxygen.
• Equipment Problems Or Operator Errors That Occur Downstream Are Not
Prevented By These Devices.
• Do Not Guard Against Accidents From Crossovers In The Pipeline System Or A
Cylinder Containing The Wrong Gas

20. Intermediate-pressure system

21. SECOND STAGE PRESSURE REGULATOR
• Some machines have pressure regulators in the intermediate
pressure system just upstream of flow indicators.
• These receive gas from either the pipeline or the pressure regulator
and reduce it further to around 26 psi for nitrous oxide and 14 psi
for oxygen.
• purpose of this pressure regulator is to eliminate fluctuations in
pressure supplied to the flow indicators caused by fluctuations in
pipeline pressure.
• not present in every workstation.

22. Intermediate-pressure system

23. Most Ohmeda Machines Have A Second-stage Oxygen
Pressure Regulator Set At A Specific Value Ranging From 12
To 19 Psig.
• Oxygen Flowmeter Output Is Constant When The Oxygen
Supply Pressure Exceeds The Set Value
• Pressure-sensor Shut-off Valves Are Set At A Higher
Threshold Value (20–30 Psig)
• Ensures That Oxygen Is The Last Gas Flow To Decrease If
Oxygen Pressure Fails.

24. OXYGEN FLUSH
• Oxygen Flush Receives Oxygen From Pipeline
Inlet Or Cylinder Pressure Regulator And Directs
A High Unmetered Flow Directly To The Common
Gas Outlet.
• The Anesthesia Workstation Requires That
Oxygen Flush Be A Single-purpose, Self-closing
Device Operable With One Hand And Designed
To Minimize Unintentional Activation.
• Flow Of 35 To 75 L/Minute Must Be Delivered

25. Intermediate-pressure system

26. Its Activation May Or May Not Result In Other Gas Flows Being Shut
Off
• May Result In Either A Positive Or Negative Pressure In Machine
Circuit.
• Pressure Is Transmitted Back To Other Structures In Machine, And
May Change The Vaporizer Output And The Flow Indicator Readings
• The Anesthesia Workstation Standard Requires That The
Connection Of The Flush Valve Delivery Line To The Common Gas
Outlet Be Designed So That Activation Does Not Increase Or
Decrease The Pressure At The Vaporizer Outlet By More Than 10
Kpa Or Increase The Vapor Output By More Than 20%

27. HAZARDS
• Accidental Activation And Internal Leakage.
• Flush Valve May Stick In On Position
• Barotrauma And Awareness
• Activation During Inspiration Delivered By The Anesthesia
Ventilator Results In Delivery Of High Tidal Volumes And
Hence Barotrauma May Occur.

28. FLOW ADJUSTMENT CONTROL
• Regulates Flow Of Oxygen, Air, And Other Gases To The
Flow Indicators.
• Mechanical And Electronic.
• Anesthesia Workstation Standard Requires That There Be
Only One Flow Control For Each Gas.
• Must Be Adjacent To Or Identifiable With Its Flowmeter.

29. MECHANICAL FLOW CONTROL VALVE
Controls Rate Of Gas Flow Through Its Associated Flowmeter.
COMPONENTS :
• Body
• Stem And Seat
• The stem and seat have fine threads so that the stem moves
only a short distance when a complete turn is made.
• When the valve is closed, the pin at the end of the stem fits
into the seat, occluding the orifice so that no gas can pass
through the valve.
• The greater the space between the pin and the seat, the
greater the volume of gas that can flow.
• To eliminate any looseness in the threads, the valve may be
spring loaded

30. CONTROL KNOB
• Control Knob Is Joined To The Stem
• Oxygen Flow Control Knob Is Fluted And
Large
• All Other Flow Control Knobs Must Be
Round
• Accidental Changes In Position Can Also Be
Minimized By A Shield, Bar, Or Other
Protective Barrier And By Placing Them
High Above The Working Surface To Lessen
The Likelihood Of Contact With Objects On
That Surface

31. Knob Should Be Turned Clockwise Only Until The Gas
Flow Ceases
• Further Tightening May Damage To The Pin Or Seat.
• Sometimes, Flow Control Valve Remains Open When The
Machine Is Cleaned Or Moved.
• If Gas Supply To Open Flow Control Valve Is Restored And
Associated Flow Indicator Is Not Observed, Indicator May Rise
To Top Of The Tube Where Its Presence May Not Be Noticed.
• The Sudden Indicator Rise May Damage It And Impair The
Flowmeter Accuracy.

32. Flow Control Valves Should Be Closed When Not In Use
• If There Is No Yoke Plug Or Cylinder In The Yoke Or The One-way
Valve In The Pipeline Inlet Does Not Work Well, Gas From An
Unused Gas System Could Flow Retrograde Through A
Flowmeter With An Open Flow Control Valve And Leak To
Atmosphere.
• The Stem Or Seat Can Block The Flow.

33. ELECTRONIC FLOW CONTROL DEVICE
• Electronically Activated Flow Control Devices Can Be Used To Alter Gas Flows
• Knob Is Turned Clockwise To Increase The Flow
• Flow Adjustment May Utilize A Solenoid Valve
• Usually A Mixing Area Collects The Gas Mixture
• One Control Alters Oxygen Concentration And Another Control The Total Flow
• If Less Than 100% Oxygen Is Desired, The Difference Is Made Up From The
Second Gas
• Flow And Pressure Transducers As Well As Temperature Sensors Are Used To
Maintain Accuracy.

34. THANK YOU

35. The Oxygen Ratio Monitor Controller (ORM [Newer] Or
ORMC, Both By Dräger) Shuts Off Nitrous Oxide When
Oxygen Pressure Is Less Than 10 Psi.
• The Newest Dräger Machine, The Fabius Gs, Uses A
Sensitive Oxygen Ratio Controller (S-orc).
• It's Fail-safe Component Shuts Off Nitrous Oxide If The
Oxygen Flow Is Less Than 200 Ml/Min, Or If The Oxygen
Fresh Gas Valve Is Closed.