Diameter of pressure tappings

Nominal inside pipe diameter, in Maximum diameter of pressure tap, mm (in) Radius of hole-edge rounding, mm (in)... 

A typical sharp-edged orifice is shown in Fig. 3.2-4. A machined and drilled plate having a hole of diameter Dq is mounted between two flanges in a pipe of diameter Z>,. Pressure taps at point 1 upstream and 2 downstream measure p, — Pz- The exact positions of the two taps are somewhat arbitrary, and in one type of meter the taps are installed about 1 pipe diameter upstream and 0.3 to 0.8 pipe diameter downstream. The fluid stream, once past the orifice plate, forms a vena contracta or free-flowing jet. 

Orifice. Equation (M-13) is used for measuring the flow rate of water with orifice and Eq. (M-14) for measuring the rate of flow of air. Interim Supplement 19.5 on Fluid Meters gives the tables of the values of discharge coefficient C for various pipe diameters as a function of diameter ratio P and pipe Reynolds number R, based on orifice diameter d. Excerpts from the tables in the Supplement are given in Table M-7 for the three types of pressure-tap locations. The values below the stepped line are extrapolations and are subject to larger tolerance as given in Table II-V-1 in the Supplement. 

Flow Nozzles A simple form of flow nozzle is shown in Fig. 10-17. It consists essentially of a short cylinder with a flared approach section. The approach cross section is preferably elliptical in shape but may be conical. Recommended contours for long-radius flow nozzles are given in ASME PTC, op. cit., p. 13. In general, the length of the straight portion of the throat is about one-h f throat diameter, the upstream pressure tap is located about one pipe diameter from the nozzle inlet face, and the downstream pressure tap about one-half pipe diameter from the inlet face. For subsonic flow, the pressures at points 2 and 3 will be practically identical. If a conical inlet is preferred, the inlet and throat geometry specified for a Herschel-type venturi meter can be used, omitting the expansion section. 

Pressure Measurement Although successful pressure-measurement probes or taps have been fabricated by using porous materials, the most universally accepted pressure tap consists of a purged tube projecting into the bed as nearly vertic ly as possible. Minimum internal diameters are 1 to 2 cm (V2 to 1 in). A purge rate of at least 0.9 m/s (3 ft/s) is usually required. Pressure measurements taken at various heights in the bed are used to determine bed level. 

The core - flood apparatus is illustrated in Figure 1. The system consists of two positive displacement pumps with their respective metering controls which are connected through 1/8 inch stainless steel tubing to a cross joint and subsequently to the inlet end of a coreholder 35 cm. long and 4 cm. in diameter. Online filters of 7 im size were used to filter the polymer and brine solutions. A bypass line was used to inject a slug of surfactant solution. Two Validyne pressure transducers with appropriate capacity diaphragms are connected to the system. One of these measured differential pressure between the two pressure taps located about one centimeter from either end of the coreholder, and the other recorded the total pressure drop across the core and was directly connected to the inlet line. A two - channel linear strip chart recorder provided a continuous trace of the pressures. An automatic fraction collector was used to collect the effluent fluids. 

An inclined manometer is used to measure the pressure drop between two taps on a pipe carrying water, as shown in Fig. 4-P13. The manometer fluid is an oil with SG = 0.92, and the manometer reading (L) is 8 in. The manometer reservoir is 4 in. in diameter, the tubing is 4 in. in diameter, and the manometer tube is inclined at an angle of 30° to the horizontal. The pipe is inclined at 20° to the horizontal, and the pressure taps are 40 in. apart. 

A 2 in. sch 40 pipe carries a 35° API distillate at 50°F (SG = 0.85). The flow rate is measured by an orifice meter which has a diameter of 1.5 in. The pressure drop across the orifice plate is measured by a water manometer connected to flange taps. 

An orifice meter is installed in a 6 in. ID pipeline that is inclined upward at an angle of 10° from the horizontal. Benzene is flowing in the pipeline at the flow rate of 10 gpm. The orifice diameter is 3.5 in., and the orifice pressure taps are 9 in. apart. 

An orifice meter is installed in a vertical section of a piping system, in which SAE 10 lube oil is flowing upward (at 100°F). The pipe is 2 in. sch 40, and the orifice diameter is 1 in. The pressure drop across the orifice is measured by a manometer containing mercury as the manometer fluid. The pressure taps are pipe taps (2j in. ID upstream and 8 in. ID downstream), and the manometer reading is 3 in. What is the flow rate of the oil in the pipe, in gpm ... 

The coefficient of discharge Cd for a particular orifice meter is a function of the location of the pressure taps, the ratio of the diameter of the orifice to the inside diameter of the pipe dJdY, the Reynolds number in the pipeline Re, and the thickness of the orifice plate. 

Water flows upwards at a speed of 2 m/s in a vertical pipe. A Venturi meter having a throat diameter equal to half the pipe diameter is fitted in the pipe and has pressure taps connected to a mercury manometer. The distance between the pressure taps is 50 mm. If the discharge coefficient of the Venturi is 0.98, what will... 

The pressure drop for the produced carrier or catalyst is measured in the setup shown in Fig. 10. An adjustable flow rate of 300-700 Nm3/h ambient air is supplied by a blower and passed downwards through a bed of catalyst in a long tube. The diameter of the bed is 0.39 m, which is well above the minimum of 10 pellet diameters required for satisfactory reproduction of the void fraction observed in a large fixed bed. The catalyst is poured into the tube from the top and the bed may subsequently be settled by applying a reproducible tapping or vibration to the tube. Since the latter reduces the void and increases the pressure drop, it is important that the catalysts are loaded and vibrated in the same way in order to get comparable results. The pressure drop without catalyst should be checked in order not to introduce errors from the support grid or measuring taps. 

The use of tapped holes in pressure parts shall be minimized. To prevent leakage in pressure sections of casings, metal, equal in thiekness to at least half the nominal bolt or stud diameter, in addition to the allowance for corrosion, shall be left around and below the bottom of drilled and tapped holes. The depth of the tapped holes shall be at least... 

Figure 17.8 shows the probe, which consists of a 1-millimeter diameter t3rpe K thermocouple centered between two 1-millimeter diameter pressure taps. Each of the pressure tubes was bent 90° and sheared at the bend. To obtain a measurement, the tube is rotated until the pressure difference between the two taps is maximized. This is the position at which one tube is directed into the oncoming flow and the other is parallel to it. The approach flow thus observes an approximately 1-millimeter thick planar obstruction. The pressure difference and temperature are then recorded. The pressure difference is related to the approach velocity, and the angle determines the tangential and axial velocity components in this case. The local mass flux is then determined from the axial velocity component and the temperature (necessary to compute the flow density), and... 

Recommendations for pressure-tap dimensions are summarized in Table 10-3. Data from several references were used in arriving at these composite values. The length of a pressure-tap opening prior to any enlargement in the tap channel should be at least two tap diameters, preferably three or more. 

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