piped system

• PMGV


  Piped Medical Gas And Vacuum system where gases are delivered from central supply points to different sites in the hospital at a pressure of about 400 kPa
• PMGV


  • Special outlet valves supply the various needs throughout the hospital
  • Oxygen, nitrous oxide, Entonox, compressed air and medical vacuum are commonly supplied through the pipeline system
• PMGV Components


  • Central supply points such as cylinder banks or liquid oxygen storage tank
  • Pipework made of special high-quality copper alloy
  • Fittings made from brass and brazed rather than soldered
  • Outlets identified by gas colour coding, gas name and by shape
  • Outlets can be installed as flush-fitting units, surface-fitting units, on booms or pendants, or suspended on a hose and gang mounted
  • Isolating valves behind break glass covers positioned at strategic points throughout the pipeline network
• Flexible hose connection


  Anaesthetic machine end should be permanently fixed using a nut and liner union where the thread is gas specific and non-interchangeable (NIST)
• PMGV Problems and safety features


  • Reserve bank of cylinders available should the primary supply fail
  • Low pressure alarms detect gas supply failure
  • Single hose test to detect cross-connection
  • Tug test to detect misconnection
  • Regular repair and modification enforced
  • Anaesthetists responsible for gases supplied from terminal outlet to anaesthetic machine
  • Pharmacy, supplies and engineering departments responsible for gas pipelines 'behind the wall'
  • Risk of fire from worn or damaged hoses
• Pressure gauge


  Measures the pressure in the cylinder or pipeline
• Pressure gauge components


  • Robust, flexible and coiled tube which is oval in cross-section
  • Tube sealed at inner end and connected to a needle pointer which moves over a dial
  • Other end of tube exposed to the gas supply
• Pressure gauge mechanism


  1. High-pressure gas causes the tube to uncoil (pressure acts to straighten a coiled tube)

  2. Movement of the tube causes the needle pointer to move on the calibrated dial indicating the pressure
• Pressure gauge problems and safety features


  • Each pressure gauge colour coded and calibrated for a particular gas or vapour
  • Pressure gauge designed for pipelines should not be used to measure cylinder pressure and vice versa
  • Should the coiled tube rupture, the gas vents from the back of the pressure gauge casing
  • Face of the pressure gauge made of heavy glass as an additional safety feature
• Pressure regulator (reducing valve)


  Reduces the variable cylinder pressure to a constant safer operating pressure of about 400 kPa
• Pressure regulator advantages


  • Protects the components of the anaesthetic machine against pressure surges
  • Allows low-pressure piping and connectors to be used in the machine, making the consequences of any gas leak much less serious
• Pressure regulator components


  • Inlet, with a filter, leading to a high-pressure chamber with a valve
  • Valve leading to a low pressure chamber and outlet
  • Diaphragm attached to a spring situated in the low pressure chamber
• Pressure regulator mechanism


  1. Gas enters the high-pressure chamber and passes into the low-pressure chamber via the valve

  2. Force exerted by the high-pressure gas tries to close the valve, opposing force of the diaphragm and spring tries to open the valve

  3. Balance reached between the two opposing forces maintains a gas flow under a constant pressure of about 400 kPa
• Pressure regulator problems and safety features


  • Formation of ice inside the regulator can occur
  • Diaphragm can rupture
  • Relief valves (usually set at 700 kPa) fitted downstream of the regulators allow the escape of gas should the regulators fail
  • One-way valve positioned within the cylinder supply line prevents backflow and loss of gas from the pipeline supplies should a cylinder not be connected