Automatic vents

Most small Hquid helium containers are unpressurized heat leak slowly bods away the Hquid, and the vapor is vented to the atmosphere. To prevent plugging of the vent lines with solidified air, check valves of some sort are included in the vent system. Containers used for air transportation are equipped with automatic venting valves that maintain a constant absolute pressure with the helium container in order to prevent Hquid flash losses at the lower pressures of flight altitudes and to prevent the inhalation of air as the pressure increases during the aircraft s descent. Improved super insulation has removed the need for Hquid nitrogen shielding from almost all small containers. 

Most refinery process units and equipment are manifolded into a collection unit, called the blowdown system. Blowdown systems provide for the safe handling and disposal of liquids and gases that are either automatically vented from the process units through pressure relief valves, or that are manually drawn from units. Recirculated process streams and cooling water streams are often manually purged to prevent the continued buildup of contaminants in the stream. Part or all of the contents of equipment can also be purged to the blowdown system prior to shutdown before normal or emergency shutdowns. 

Accumulation of Noncondensihles - Noncondensibles do not accumulate under normal conditions since they are released with the process vapor streams. However, with certain piping configurations, it is possible for noncondensibles to accumulate to the point that a condenser is "blocked". Such a condition could occur if an automatic vent control valve failed closed for a period of time. This effect is equal to a total loss of coolant, and thus need not be considered separately. 

When injecting air in pressure mains, it must be taken into account that the volume of oxygen only amounts to about 20%. The inert N2 gas — to some extent mixed with the incoming air—will be collected at the top part of a pipe. An automatic vent system to remove this gas may be installed. The pumping performance of an air-injected pressure main can be evaluated using a model for the energy loss. 

The cross-section of a typical mercury button cell is shown in Fig. 3.24. The cathode and anode current collectors are the steel case and steel top, respectively. Attention is drawn to the sophisticated engineering design of this cell, which has provision for automatic venting of any pressure caused by hydrogen evolution, with any electrolyte displaced being absorbed in the safety sleeve between the inner and outer case. 

In addition to reducing the probability of a dust explosion, it is possible to take steps to mitigate the consequences of a dust explosion, should one occur. Use of automatic vents to prevent the buildup of destructive overpressures and constructing areas with blowout partitions are examples of such steps. Also, spaces which may contain these high dust concentrations can be kept fairly open to minimize the development of turbulence in a flame front, should an explosion occur. 

The secondary relief device is usually sized to a much lower discharge rate than the primary. The secondary relief device can be a safety valve, a bursting disk, an automatic pressure-controlled vent valve, or a high-pressiu-e switch that opens an automatic vent. If the secondary device is a relief V2dve or a bursting disk, credit for its rate of discharge can be teiken when sizing the primary relief device. 

Accumulation of noncondensables in the drum may unflood the drum and interrupt the control action. If noncondensables accumulation is infrequent, manual venting from the top of the drum will be sufficient to restore satisfactory operation. If noncondensables accumulate frequently, or the column is nm imattended, automatic venting is required. 

Figure 17.5c illustrates an automatic vent system that worked well (203). A second pressure controller (PC No. 2), a level controller, and a control valve in the vent line are added. The set point of PC No. 2 is lower than that of the normal pressure controller (PC No. 1). When the drum is full, the level controller keeps PC No. 2 tripped off, and the vent valve is closed. Drum unflooding (due to noncondensable accumulation) is sensed by a drop in drum level. The lower level activates PC No. 2. Since the set point of PC No. 2 is lower than PC No. 1, it opens the vent valve. As the pressure falls, PC No. 1 closes, helping to build up the drum level. As soon as the drum refills, the level controller trips PC No. 2, and the vent valve closes. 

A simple automatic venting system was developed and solved the problem. 

Passive protection refers to protecting a bnilding by attempting to confine a fire to the area in which it started. Automatic venting orblocking of the products of combustion is involved. 

The automatic vent on the blower discharge was overhauled to prevent unintended leakage of process air. 

Moving cores can be selectively controlled using this technique so that they automatically open or close, depending on the position of the melt. This is for example used in automatic venting of cavities by only closing a moving core when the cavity is almost completely filled. 

Explosion doors open in case of an explosion, thereby releasing the vent area. Depending on the application, explosion doors may be selected which remain open or close automatically after releasing the explosion. 

Install flame arresters on atmospheric vents to prevent fire on the outside of the tank from propagating back into the vapor space inside the tank. Provide fire resistant insulation for critical vessels, piping, outlet valves on tanks, valve actuators, instruments lines, and key electrical facilities. Provide remote controlled, automatic, and fire-actuated valves to stop loss of tank contents during an emergency provide fire protection to these valves. Valves should be close-coupled to the tank, and must be resistant to corrosion or other deleterious effects of spilled fluids. Vessels should be provided with overpressure relief protection. 

Design ventilation system to keep flammable concentration below lower flammable limit Provide on-line flammable gas detection and activation of inerting system Install automatic sprinkler system Install deflagration vents... 

Provide automatic sprinkler system/inerting gas Provide deflagration vents Provide deflagration suppression system Monitor flammable atmosphere/fire Provide nitrogen blocks (nitrogen injection to stop flame propagation) or other explosion isolation measures... 

Provide automatic sprinkler system Use deflagration vents... 

The use of appropriate instruments to monitor equipment operation and relevant process variables will detect, and provide warning of, undesirable excursions. Otherwise tliese can result in equipment failure or escape of chemicals, e.g. due to atmospheric venting, leakage or spillage. Instruments may facilitate automatic control, emergency action such as coolant or pressure relief or emergency shutdown, or the operation of water deluge systems. 

Oxygen 0, Severe metallic corrosion Addition of corrosion inhibitors, sodium sulfite Automatic air vents, deaeration... 

The Code [26] allows pilot operated vent control valves provided the vent valve can operate automatically in case the pilot valves/system failed. 

Whatever automatic start-up method is adopted, steam will only flow into the mains and discharge air from the air vents at a pressure at least a little above atmospheric. It then reaches the pipe and condenses on the cold metal, and at first the condensate temperature will be well below 100°C (212°F). This means that the steam traps will have a greater capacity than their normal rating when handling saturated condensate. If the traps are fitted to a collecting leg, at about 700 mm below the main, then filling of the collecting leg will provide a hydraulic head of about 0.07 bar or 1 Ib/in in addition to the line pressure. 

This means that thermostatic balanced pressure steam traps which open when their element senses a temperature somewhat below that of saturated steam at the pressure existing within the steam space are very effective when used as automatic air vents. They are connected to a steam space at any location where air will collect. Usually this means at any remote point from the steam entry, along the path the steam takes as it fills the steam space. 

The opportunity is taken, while filling for testing, to ensure that the circuits can be filled without airlocks. Air vents at high points of the circuit may be automatic or manual. While the pipes are full, pumps should be run if possible to dislodge any dirt before draining down and cleaning the strainers. If a lot of dirt is found, the pipework should be filled again and reflushed. In any case, the pumps should be run at the earliest opportunity and the strainers cleaned out. 

Automatic gas purgers comprise a collection vessel for the gas mixture with an inhuilt cooling coil connected to the main suction, or with its own refrigeration system. Condensed refrigerant returns to the condenser, and any gas remaining in the vessel will he non-condensihle and can he vented hy an inverted bucket trap. 

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