Backpressure devices

The detector inlet usually passes through a coiled stainless steel tubing heat exchanger and into the flow cell. The flow cell is the most complicated part in the system. The body is stainless steel or quartz, windows are quartz, and, if it can be taken apart for cleaning, there is usually a Teflon gasket between the stainless steel body and the quartz window. Finally, we move out of the flow cell into the wide-diameter Teflon tubing of the outlet tubing and into a backpressure device in the waste vessel. 

VW 5. Air bubbles in detector. 5. Purge detector. Install backpressure device after detector. 

Safety Relief Valves Conventional safety relier valves (Fig. 26-14) are used in systems where built-up backpressures typically do not exceed 10 percent of the set pressure. The spring setting or the valve is reduced by the amount of superimposed backpressure expecied. Higher built-up backpressures can result in a complete loss of continuous valve capacity. The designer must examine the effects of other relieving devices connected to a common header on the performance of each valve. Some mechanical considerations of conventional relief valves are presented in the ASME code however, the manufacturer should be consulted for specific details. 

First and foremost these venting ducts should be as straight as possible, with few, if any elbows, and even these should be sweeping bends. There should be no valves of any type to keep flow resistance as low as possible, as this creates friction that creates backpressure on the relief device and raises burst conditions, which can be terribly dangerous. Figure 7-66 and 7-67 are used to assess the increased pressure due to ducts on relief discharge as affected by duct length. (This data is limited. See Ref. [56 and 53].)... 

HRSG), a furnace or a NO treatment unit. The backpressure created by such a device decreases the power generation. Even if there is no device, changes in elevation changing the ambient pressure also change the machine performance. 

Backpressure The pressure at the outlet of the relief device during the relief process resulting from pressure in the discharge system. 

A relief device must be designed for a vessel to relieve 1800 gpm of crude oil liquid in the event that a discharge line is blocked. The MAWP is 250 psig, and a maximum backpressure of 50 psig is expected. The specific gravity of the oil is 0.928, and its viscosity is 0.004 kg/m s. 

A relief device must be installed on a vessel to protect against an operational upset. The relief must discharge 53,500 lb/hr of hydrocarbon vapor. The relief temperature is 167°F, and the set pressure is 75 psig. Assume an overpressure of 10% and a backpressure of 0 psig. The hydrocarbon vapor has a molecular weight of 65, a compressibility of 0.84, and a heat capacity ratio of 1.09. Determine the diameter of the relief. 

Backpressure The pressure existing at the outlet of a relief device. The value under no-flow conditions is superimposed backpressure. The value under flowing conditions consists of both... 

Superimposed backpressure The static pressure existing at the outlet of a pressure relief device at the time the device is required to operate. It is the result... 

The eventual supplementary balancing piston is actually fitted as a backup device if the bellows fail in service this device will ensure that the valve still relieves at the correct set pressure. Balancing piston valves are uncommon and expensive, but without the balancing piston fitted, the variable backpressure has an adverse effect on the set point of the SRV. This may result in the valve not relieving at its hill capacity or not achieving hill lift within 10% overpressure... 

There are two kinds of discharge systems open and closed. Open systems discharge directly into the atmosphere, whereas closed systems discharge into a manifold or other fluid recuperation device, eventually, along with other SRVs. Both systems can create backpressures, which need to be taken into account at all times when sizing and selecting the correct SRV. 

When smaller porous particles are used, the result is a highly efficient packed column with smaller interspatial voids however, this leads to lower permeability of the column, and high backpressures are often generated. To overcome these problems, polymeric monoliths have been developed these are a continuous phase of porous material that can be used without generating the high backpressures observed with fine particles. These systems, popularized by Frechet and Svec, have found application both in separation devices [110] and, more recently, as flow reactors [111-113],... 

This device, generally known as a continuous-pressure type, is basically a double check valve with an atmospheric vent located between the checks (Fig. 6). In a backpressure condition (downstream pressure exceeds supply pressure) or a backsiphonage condition (supply pressure drops to atmospheric or lower), both checks close and... 

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