Orifice restriction

In the restriction orifice, no pressure measuring devices are installed, and the pressure drop is estimated as an actual pressure drop without the consideration of any pressure recovery. For this reason, the discharge coefficient for the restriction orifice is generally higher in comparison to other orifice flow measuring devices. The coefficient is also independent on Reynolds number. Values of discharge coefficient for restriction orifices are available in the literature [3]. For simplicity, this can be presented as  

Process engineering and design using Visual Basic 

In the Venturi meter, the fluid is passed through converging/diverging sections, and because of gradual reduction of area, there is no vena contracta. The coefficient of discharge is in the range of 0.98 to 0.99 [2]. 

---

Install mechanical flow restriction (e.g., restriction orifice) of utility with open vent on vessel... 

Excessive fill rate. Install flow restriction orifice in fill line... 

The pumps can be either centrifugal or positive displacement types. The centrifugal pumps should have a head curve continuously rising toward the shut-off point. The standby pump should be piped into the system in a manner that permits checking of the pump while the main pump is in operation. To achieve this, a restriction orifice is required with a test bleeder valve piped to the return oil line or the reservoir. 

Restriction Orifice - In general a restriction orifice should not be used as a means of limiting the capacity of a pressurization path. In special cases, where large incentives apply (such as reducing die size of a flare system), a restriction orifice may be used, provided that all the following conditions are satisfied ... 

Limit the total possible charge to a batch reactor by using a precharge or feed tank of limited capacity. Alternatively, limit the addition rate by selecting a pump with a maximum capacity lower than the safe maximum addition rate for the process, or by using restriction orifices. 

Use physical limits of pipe size, restrictive orifices, and pump sizing to limit excessive flow rates. 

Positive pumps are normally fitted with relief valves. These are not usually fitted to centrifugal pumps unless the process material is likely to explode if it gets too hot. As an alternative to a relief valve, such pumps may be fitted with a high-temperature trip. This isolates the power supply. Or a kick-back, a small-diameter line (or a line with a restrietion orifice plate) leading from the delivery line baek to the suction vessel, may be used. The line or orifice plate is sized so that it will pass just enough liquid to prevent the pump from overheating. Small-diameter tines are better than restriction orifice plates as they are less easily removed. 

Restriction orifices with upstream pressure regulators are frequently employed to distribute aeration gas into the standpipes. The orifices... 

Once the unit is running well, it is often assumed that the aeration system is sized properly, but changes in the catalyst physical properties and/or catalyst circulation rate may require a different purge rate. It should be noted that aeration rate is directly proportional to catalyst circulation rate. Trends of the E-cat properties can indicate changes in the particle size distribution, which may require changes in the aeration rate. Restriction orifices could be oversized, undersized, or plugged with catalyst, resulting in over-aeration, under-aeration, or no aeration. All these phenomena cause low pressure buildup and low slide valve differential. 

Improperly designed, eroded, or even missing restriction orifices used for steam purge or aeration nozzles could cause catalyst attrition. Catalyst attrition is also caused by broken air and stripping steam distributors. 

Confirm that the restriction orifices used for instrument purges are in proper working condition and that the orifices are not missing. 

Care should be taken not to flood the feed nozzles since this adversely influences atomization. This happens when too little steam is used or too much feed is injected to a nozzle. Restriction orifices nsed in feed and steam lines may need to be replaced. Strainers on these lines might reqnire periodic cleaning. 

It becomes evident that accurate sampling requires a constant flow rate. Many methods have been used in the attept to provide a constant flow sampler, including rotometers, motor-voltage regulators, restricting orifices, pump stroke-counters and motor-current compensation. These methods attempt to provide compensation indirectly for the error effects (5 ). 

Venting the channel head through the balance line shown in Fig. 8.6 will prevent an excessive accumulation of C02. This is done by continuous venting from the top of the condensate drum. For every 10,000 lb/h of steam flow, vent off 50 lb/h of vapor through a restriction orifice, placed in the condensate drum vent. This is usually cheaper than controlling reboiler steam-side corrosion, with neutralizing chemicals. 

Usually, only a small amount of the heating steam—specifically, stripping steam—is vented through the restriction orifice, out the atmospheric vent. It is this small stripping steam flow that drives the air out of the soft water. 

Plasma Arc Welding. In the transferred-arc mode of the PAW process, shown in Figure lc, the arc is between a nonconsumable electrode and the base metal, in a manner similar to the GTAW process. The unique feature is the flow of inert gas around the electrode and through a restricted orifice, which constricts the arc to form a plasma jet. A second, outer stream of shielding gas protects the molten metal from atmospheric contamination. In the nontransferred arc mode of the PAW process, the arc is between the electrode and the constricting orifice. This mode is used for plasma spraying... 

Cavitation occurs when bubbles containing either vapor or gas are formed by reduction in the local pressure at constant temperature (Brennan, 1995 Knapp et al., 1979 Young, 1989) such as the rapid movement of the fluid past an impeller blade, through a pump, or in this case through a restriction (orifice) at near supersonic velocities. Quantifying the cavitation number is debatable, but it can be derived from the Bernoulli equation. Lush (Young, 1989) uses a throat cavitation number (aT) defined as... 

Calculations were made. Engineers figured that a vent of about 30 inches (76 cm) in diameter would have prevented the destructive vacuum from collapsing the tank during the ammonia absorption incident. A giant-sized vent was impractical for this installation, hence they concluded that water should be added slowly through a restrictive orifice. [8]... 

Line blind Figure 8 blind Restriction orifice (figd) Restriction orifice (union) Removable type orifice... 

Restriction Orifice Plates Not Installed Cross Connection of Systems... 

---