Ventilation manometer

In ventilation applications, where the density of the manometer fluid is much higher than the density of air, the pressure difference Ap can be expressed using the equation... 

The most frequently applied mechanical manometers in ventilation applications are fluid manometers, bur the following types are also used. The Bourdon tube is a small-voiume tube with an elliptic cross-section bent to the shape of a circular arc, the C-type. One end is open to the applied pressure while the other end is closed. The pressure inside the tube causes an elastic defonnation ot the tube and displaces the closed end, which is then converted, by means of a linkage mechanism, into the movement of a pointer. The Bourdon tube may be of a spiral or helical design as well. 

Electrical manometers have developed during the last 30 years. Modern electrical manometers are well suited for ventilation applications, both in the laboratory and in the field. The advantage of this type of instrument is fhat they are sensitive enough to measure small pressure differences with electrical output, enabling monitoring. A convenient feature, especially in the field is that the instrument is hand-held and there is no need for leveling on a bench, as for fluid manometers. The conversion of the pressure difference into an electrical signal can be based on several different phenomena. 

As well as measurement errors due to the pressure measurement instrument itself, other errors related to pressure measurements must be considered. In ventilation applications a frequently measured quantity is the duct static pressure. This is determined by drilling in the duct a hole or holes in which a metal tube is secured. The rubber tube of the manometer is attached to the metal tube, and the pressure difference between the hole and the environment or some other pressure is measured. 

All laboratories with exposed mercury surfaces, such as in beakers used as the open limbs of manometers, must have good ventilation, particularly in colder climates where windows are usually shut and normal ventilation is often very poor. 

All ventilation systems should have a device that readily permits the user to monitor whether the total system and its essential components are functioning properly. Manometer, pressure gauges, and other devices that measure the static pressure in the air ducts are sometimes used to reduce the need to manually measure airflow. "Telltales" and other similar simple devices can also serve as indicators of airflow. The need for and the type of monitoring device should be determined on a case-by-case basis. If the substance of interest has excellent warning properties and the consequence of overexposure is minimal, the system will need less stringent control than if the substance is highly toxic or has poor warning properties. 

The easiest check on system performance is to check the static pressnre at the hood throat (or throats), the point where the duct leaves the hood. This is simply the difference between pressure in the duct and atmosphere, and can be measured with a manometer -at its simplest a U-tube of liquid, although electronic versions are available. The dnct-work can have removable caps at pressure check points. Records shonld be kept of ventilation system checks. 

Keywords— manometric technique, nasogastric tube placement, mechanically ventilated patients, manometer, accuracy. 

This study has demonstrated that the manometric technique using a cuff pressure manometer can accurately verily NGT placement in intubated, mechanically ventilated patients. In the aim of gastric decompression or in settings where roentgenograms are not available, the manometric technique is a convenient, inexpensive and highly accurate method to verily NGT placement. This technique may have the potential to reduce the complications of NGT placement and improve patient safety. 

The gas (air) from the ventilator (1) measured by the diaphragm (2) and its differential manometer (4) entere the column (7). As well known, under the loading point the gas velocity does not influence the liquid-side cantrolled processes. A proper velocity wlue is abcnit 0.5 m/s... 

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