a. Gas regulator: pressure-reducing valve that uses opposing forces on two side of a diaphragm. Regulators are used in piping systems, on cylinders and inside ventilators toi. Maintain a constant pressure because the pressure from the tanks will decline with useb. Direct action regulators: this regulator operates with a spring-loaded diaphragm that opposes the pressure of the gas. The opposition of the force of the spring and the pressure of the gas keeps the pressure downstream from the regulator at a constant pressure.
ii. Reduce a high pressure to a lower one. Many regulators reduce the cylinder's 2000 psig to the 50-60 working pressure needed for respiratory care equipmentc. Indirect action regulators: works the same way, the gas flows differentlyi. When the poppet is at rest, it is closed against the door that leads to the higher pressure chamber. The lower pressure chamber starts to empty
ii. Once the pressure in the lower chamber drops below the spring tension, the diaphragm moves the poppet into the high-pressure chamber. This opens the door. Gas flows from the higher pressure chamber into the lower pressure chamber until it equals the spring tension.
iii. Then the poppet closes and the flow stops
iv. To keep the pressure constant: if the pressure upstream drops, the poppet opens to allow gas to enter until the pressure equals the spring tension
v. The diaphragm position and its regulation of the pressure are determined by the position of the spring.
d. Single-stage regulators: the regulator reduces the pressure only in one step
e. Dual stage regulators: the regulator reduces the pressure with two single stage regulators in series so that the pressure goes from highest to a working pressure. This will have two pressure relief valves
One determines how many stages a given regulator has by counting the pressure relief valves.
f. Multi-stage regulators: more than two single stage regulators in series will have as many stages as there are pressure relief valves.
g. Adjustable regulators: Some springs are preset at the factory and others are set by the operator. The regulator in pp. 60 Figure 3-2 is adjustable because the spring is attached to a handle that can be turned to tighten or loosen the tension.
h. Preset regulators: will not have the adjustment handle. The tension of each spring will never vary. The regulator in pp. 60 Figure 3-2 is pre-set at the factory.
i. Pressure relief valves: when the pressure in a regulator exceeds the appropriate pressure by 50%, the spring disc opens to vent the chamber to the atmosphere. There is one pressure relief valve per reducing stage. Over-pressure tends to happen when there is trash downstream from the regulator causing decreased flow out of the regulator.
j. Pressure gauges: manometers are devices used to measure pressure in line or in tanks. In medical gases, these are generally calibrated in psig or in kPa.
The Bourdon Gauge pressure
manometer consists of a coiled hollow tube with a closed end, which straightens
out as gas pressure inside the tube rises. The tube is attached to a series
of gears which in turn are finally to a dial that points to a pressure on the dial
a. For it to work properly to display the flow rate, it must have a fixed orifice downstream from the bourdon gauge. A fixed orifice would allow more gas through it as the pressure rises.
b. The gauge actually measures the back-pressure created by the restricted orifice.
Over the last few years, bourdon gauges on ventilators are being replaced by digital monometers with a faster response time. "If the digital monometer has been calibrated, it will always be more accurate than any bourdon gauge."
a. Does this device work upside down? Yes, there is no problem with changes in gravity like there are with the other common type of flow meter
b. Could Bourdon gauges work in the international space lab? Yes, as long as the cab was pressurized to 760 mmHg [one atmosphere] & if the space lab were heated to room temperature.
In this device, a variable orifice and a constant pressure will control the flow rate. The 02 flow meter must be placed downstream from a regulator that has reduced the pressure to 50 psig. At a constant pressure, the gas flow will rise as the orifice opens to allow more gas to enter. The orifice is controlled by a needle valve.a. The actual flow rate is measured by the rising of a float. The gas molecules push up on the float until the tube widens enough for them to get around it. As the flow rate increases, the float rises higher. As long as the flow is stronger than gravity the float will stay suspended.
b. Can this Thorpe tube be used as a flow meter? Yes, if it is at sea level and room temperature and the appropriate gas is used.
Flow meter/regulator 'click style' or flow restrictor: http://www.westernmedica.com/medicacatalog/pdfs/WG6.pdfc. Is the flow rate accurate in all conditions? No.i. Different gases have different densities and these densities will cause inaccuracies. Flow meters are gas-specific. A 02 flow meter will not be used for compressed air or for C02 delivery. If one uses a 02 flow meter to deliver Helox [02/He mixture] the RCP must make conversions for accuracy.d. Does this work up side down? While the Thorpe tube may not be read when it is turned upside down or on it's side, because the float will move, its flow rate will be constant, but one must turn the Thorpe tube back to upright to read the flow rate.1. Multiply the 02 liter flow by 1.8 to correct for 80% Helox gas or by 1.6 for 70% Helox mixtureii. The Thorpe tube must be attached to 50 psig,---if it is not, the flow rate will be inaccurate
e. The Thorpe tube would be a poor choice for the international space lab because it requires gravity to work. While the needle valve actually changes the flow rate, the float would not be responding properly and the flow meter would not be functional as a monitoring devise.i. One would do better with a bourdon gauge type of flow meter, or one would use a flow restrictor rather than a flow meter. The flow restrictor has several adjustable orifices that can be selected by turning a knob.
|The station outlet or
the regulator is leaking.
You hear a hissing sound
around the connection
The flow may or may not enter
the flow meter based on the degree of the leak
|1. Have you selected
the wrong connector for the gas?
a. Check the DISS connections of both flow meter and station outlet2. Is the quick-connect getting worn?
a. Get a new flow meter3. Is the station outlet quick-connect getting too old?
a. Call maintenance to replace the station outlet.
| The flow meter displays
you set it up & check
the flow with an Erie test flow meter to see that the flow is off
|1. Is the flow meter
compensated for back pressure?
a. Occlude the outlet and see if the flow meter indicates that the flow is higher than before. If the flow rises erroneously this is an uncompensated flow meter. Change to a compensated flow meter.2. Is there an obstruction downstream such as an entrainment device or a cool humidifier?
a. Remove the obstruction3. If the flow meter is a Thorp tube, is it up right?
a. Turn it upright to read & adjust the flow rate4. Is the flow meter running off 50 psig?
a. Use correct reducing valve/ regulator to get to 50 psig5. Is the flow meter at sea level?
a. If you are in a un-pressurized air plane cabin, change to a flow-restrictor type of flow meter or bourdon gauge type of flow meter6. Is it at room temperature?
a. Temperatures where the flow meter are inaccurate would be intolerable for other reasons so that unlikely7. Is it attached to Helox rather than 02?
a. Calculate the correct flow rate by multiplying the set flow rate by 1.8 to get the accurate flow rate.
|the gas is leaking from
you feel a leak or you hear a hiss around the flow meter's body
|1. the integrity
of the tube is disrupted
a. replace the flow meter & send it out for repair
|the flow meter is leaking from the nipple adaptor||1. tighten the nipple adaptor
2. check that the nipple adaptor is not cross-threaded
7. Differentiate between compensated and non-compensated flow meters
1. Compensated Thorpe tube flow meters are compensated for the back pressure which in the case of the bourdon gauge will cause inaccurate readings
2. The compensated Thorpe tube will read the accurate flow rate as restriction downstream from it rises. As the flow is restricted, the flowmeter will display lower and lower flows. If there is complete occlusion, there will be a zero displayed. If the resistance is removed, the flow will increase.
3. The placement of the float inside the Thorpe tube will determine whether your flow meter is compensated or non-compensated.
a. An uncompensated flow meter will have a float that is downstream from the valve. This float is subjected to atmospheric pressurei. if there is an obstruction down stream such as attaching an entrainment device onto the flow meter, the back pressure builds up and effects the float.b. A compensated flow meter will have a float that is upstream from the valve so that the float will be in contact with the wall pressure rather than the atmospheric pressure.
ii. It will rise & record an erroneously high flow rate because the density of the gas under the float has been increased.
c. A quick way to remember the compensated flow meter:
Wall... ball...valve.... patient
a. The flow is accurate in the face of an obstruction down stream. Imagine what would happen if your 02 line became occluded or pinched off? Your patient could become hypoxic.i. The compensated flow meter would show that the flow rate is zerob. If the ordered flow rate is too high for your device [such as a cool humidifier or an entrainment device], as you increase the flow, the indictor would show that the flow is not increasing as you turn it…this means there is restriction down stream
ii. The uncompensated flow meter would display an erroneously high flow rate
a. Read the label on the flow meter
b. If there's nothing written, you would attach the flow meter to the wall or the tank. As soon as the inlet is in contact with the high pressure, the float [ball] will leap to the top then fall back to the correct flow.i. The uncompensated flow meter's float will not leap up
i. because the air flowmeter is dirty and can be a fire hazard as gas enters the regulator
ii.. because Thorpe tubes are calibrated for their gas and the flows will not be accurate.
When some persons go home on 02, you may not trust them to not change the proscribed liter flow. The flow restrictor can be preset & to get a different flow rate, the home care RCP needs to change the flow restrictor's outlet.
Some flow restrictors are operated off 50 psig for the hospital or for cylinders but other flow restrictors use 20 psig pressures such as used with LOX [liquid 02 systems].
Flow restrictors are accurate only at their rated pressures
A patient with chronic hypercapnia cannot change his 02 to a dangerous level where he is no longer breathing off his hypoxic drive. With a flow restrictor, the patient will get only his proscribed liter flow--- not more--- not less
Because they are so simple to operate, flow restrictors are getting a lot of use in air transport and these are the flow meters of choice in the international space station's hospital.
a. ball float: read in the middle
b. non-rotating float: read at the top
c. skirted float: read at the top
d. plumb bob valve: read at the top
e. H type float: read at the top