Piezometer tubes

Piezometer tube An open-ended calibrated glass or plastic tube that measures the pressure in a pipe or vessel full of a fluid. 

When the static pressure in a moving fluid is to be determined, the measuring surface must be parallel to the direction of flow so that no kinetic energy is converted into pressure energy at the surface. If the fluid is flowing in a circular pipe the measuring surface must be perpendicular to the radial direction at any point. The pressure connection, which is known as a piezometer tube, should terminate flush with the wall of the pipe so that the flow is not disturbed the pressure is then measured near the walls where the velocity is a minimum and the reading would be subject only to a small error if the surface were not quite parallel to the direction of flow. A piezometer tube of narrow diameter is used for accurate measurements. 

For the flow not to be appreciably disturbed, the diameter of the instrument must not exceed about one-fiftieth of the diameter of the pipe the standard instrument (diameter 7.94 mm) should therefore not be used in pipes of less than 0.4 m diameter. An accurate measurement of the impact pressure can be obtained using a tube of very small diameter with its open end at right angles to the direction of flow hypodermic tubing is convenient for this purpose. The static pressure is measured using a single piezometer tube or a piezometer ring upstream at a distance equal approximately to the diameter of the pipe measurement should be made at least 50 diameters from any bend or obstruction. 

Static pressure. Even if a fluid is flowing, the pressure measured at right angles to its flow is called the static pressure. This is the value given by manometers or piezometer tubes and pressure gauges. 

If a piezometer tube is erected at B in Fig. 10.2, the liquid will rise in it to a height BB equal to the pressure head existing at that point. If the end of the pipe at E were closed so that no flow would take place, the height of this column would then be BM. The drop from M to B when flow occurs is due to two factors (1) that a portion of the pressure head has been converted into the velocity head which the liquid has at B, and (2) that there has been a loss of head due to fluid friction between A and B. 

It is quite evident that in the case of an open channel the hydraulic gradient coincides with the water surface, because if a piezometer tube is attached to the side of the channel, the water will rise in it until its surface is level with that of the water in the channel. 

For measuring saturated hydraulic conductivity, installation of piezometer tubes into an auger hole as big as the tube s diameter is performed without disturbing the soil. A cavity is then provided at the bottom of the pipe and water is removed from the cavity after elimination... 

Auger screw type that fits inside the piezometer tube. 

Difference between depth of the piezometer tube and the water tube = dm... 

Piezometer 4 — Wood Peg 5 — Piezometer Tube 6—Coal Scam 7—Paste 8—Cement ... 

The decrease of exposure time of the manometric hole and the volume of manometric room can help to shorten the manometric period. The manometric drill hole should be right as long as it pieces the coal seam, and the capacity of manometric room (including the radius of piezometer tube) should be decreased as much as possible. The drill hole should be sealed right after the drilling work finished, in order to shorten the exposure time of the hole wall. Or high pressure compensation gas should be injected into the room. The gas pressure in the coal seam can be rapidly determined. 

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