Valve caps

Today the most important applications are in surface coatings, including some use as French polish, as adhesives and cements, including valve capping and optical cements, for playing card finishes and for floor polishes. The material also continues to be used for hat stiffening and in the manufacture of sealing wax. 

Figure 12-6B. Double-deck valve with valve cap unloader. (Used by permission Cooper-Cameron Corporation.)...

Double-deck valves with valve cap unloaders... 

A few strokes of the piston in a dry liner may ruin the liner. When the pump does not fill by gravity or when the cylinders have been emptied by standing too long or by replacement of the piston and liner, it is essential to prime the pump through the suction valve cap openings. 

Vapor bubbles up through the sieve holes, or valve caps, on the tray deck, where the vapor comes into intimate contact with the liquid. More precisely, the fluid on the tray is a froth or foam—that is, a mix-... 

When vapor flows through a tray deck, the vapor velocity increases as the vapor flows through the small openings provided by the valve caps, or sieve holes. The energy to increase the vapor velocity comes from the pressure of the flowing vapor. A common example of this is the pressure drop we measure across an orifice plate. If we have a pipeline velocity of 2 ft/s and an orifice plate hole velocity of 40 ft/s, then the energy needed to accelerate the vapor as it flows through the orifice plate comes from the pressure drop of the vapor itself. 

One of the most frequent causes of flooding is the use of carbon steel trays. Especially when the valve caps are also carbon steel, the valves have a tendency to stick in a partially closed position. This raises the pressure drop of the vapor flowing through the valves, which, in turn, pushes up the liquid level in the downcomer draining the tray. The liquid can then back up onto the tray deck, and promote jet flood, due to entrainment. 

From the designer s point of view, the top tray of the stripper must have a several times greater number of sieve holes or valve caps on its tray deck than the bottom tray. If, however, all the trays in the stripper are identical, then either the bottom tray will leak (see Chap. 2), or the top tray will flood. Either way, stripping efficiency will suffer. 

The second way to unload a reciprocating compressor is with valve disablers. Most of the unloaders you have on your compressors are likely of this inferior type. They typically consist of steel fingers, which are pressed down through the valve-cap assembly. The fingers prevent the valve plate from moving. These valve disablers are far less costly than an adjustable clearance pocket. They may be used on both the crank and head ends of the cylinder. They can reduce the gas flow through a cylinder to zero. 

Unfortunately, valve disablers have a detrimental effect on the adiabatic compressor efficiency. This means that, even though no gas may be moving through the crank end of a cylinder, the piston is still doing work on the gas inside the crank end of the cylinder. If you would like proof, place your hand on the valve cap on such a disabled cylinder. The high temperature you will feel is wasted compression work going to useless heat. I have measured in the field that, after a cylinder end is completely disabled, it is still converting 20 percent of the former compression work to heat. 

The other problem with valve disablers is poor mechanical reliability. They get stuck inside the valve cap, especially in dirty-gas service. Once stuck, the valve—and really the entire end of the cylinder—is out of service, until the next overhaul of the reciprocating compressor. 

Ornaments, automotive parts as valve caps, oil pans, intake tubes, cooling units... 

The number of valve caps that can be fitted on a tray is at best an estimate unless a detailed tray layout is prepared. However, a standard has evolved for low- and moderate-pressure operations a 3 x 2 y2 in pattern that is the tightest arrangement available, accommodating about 14caps/ft2 (150 caps/m2). The active area does not take into account liquid-distribution areas at the inlet and outlet, nor edge losses due to support rings, nor unavailable space over tray-support beams. In smaller columns, it is possible that as much as 25 percent of the active tray area may not be available for functioning valves. For this column, which operates at low pressure, select the standard 3 x 2 /2 in pitch. 

A word of caution When the valves are exposed to a corrosive environment, it is likely that their constant movement will induce fatigue stresses, which frequently lead to the rapid deterioration of the retaining lugs and valve caps. It is not unusual to find valves missing in that part of the column where corrosive constituents are concentrated. 

This article presents a correlation lor estimating Vn, (based t)n data (Vom Cdiisclt, Inc., Bulleiiit 4900, 3rd ed., p. 28) and equations to estal)lish the maximum valve hole area md the maximum number of valve caps... 

Next, determine the valve hole area, the number of valve caps, and the c ip density. Using Eq. (4), =... 

Leave the valve cap on a cylinder until the cyfinder is ready for use, at which time the cyfinder should have been secured by a support around the upper one third of its body. Disconnect the hose or regulator, shut off the valve, and replace the cap before the cylinder is completely empty to prevent the possibility of the development of a negative pressure. Place an empty sign or label on the cylinder. 

Solvents used as the mobile phase are contained in solvent reservoirs. In their simplest forms, the reservoirs are glass bottles or flasks into which feed Lines to the pump are inserted. To remove particles from solvents, inline filters are placed on the inlets of the feed lines. Sophisticated mobile phase handling systems available commercially contain specially designed bottles with internal, conically shaped bottoms that allow small solvent volumes to be used. These handling systems also feature three or four valve caps that permit the filtration, storage, and delivery of solvents, and a stopcock for vacuum degassing. 

An improved system known as the Oxford Sure/Seal Valve cap, provided for use with Sure/Seal bottles is reported to give even greater shelf-life for the reagent. 

CONVENTIONAL SAFETY-RELIEF VALVE CAP, SCREWED------fgfe... 

Stability of shellac to UV radiation is the most important optical property. The principal application of shellac was in gramophraie records. The resin acts as a binder for about three times its weight of mineral filler. Today, the most important application of shellac is in surface coatings. It is also used in some French polish as adhesives and cements including valve capping and optical cements. Shellac is also used in the manufacture of sealing wax. 

A schematic of the distillation plate is given in Figure 12.4. In many texts the terms plate and tray are used interchangeably, but we will use the convention that the plate consists of a tray , which holds the liquid, and a vapour space , which holds the vapour. The ith plate receives a liquid flow Li. via the downcomer attached to the tray of the (i -f /)th plate above. It also receives a vapour flow , i from the (i — l)th plate below it through bubble-caps or valve caps. E is used to denote evaporation rate - the letter V for vapour has already been claimed for volume.) The boiloff from the liquid on the ith tray into the plate s vapour space is denoted B,-, while the vapour flow from... 

The vapour flow will depend on both the difference in vapour-space pressure in adjacent plates and the head of liquid above the point of vapour entry into the plate above. For a sieve plate or valve-cap plate, the point of vapour entry is the bottom of the tray, but for a bubble-cap plate the point of entry is the lower edge of the bubble-cap. For a sieve or valve-cap plate, the vapour flow will have the form ... 

A cylinder should never be emptied to a pressure lower than 172 kPa (25 psi) because the residual contents may become contaminated with air if the valve is left open. Empty cylinders should never be refilled by the user. Rather, the regulator should be removed, and the valve cap should be replaced. The cylinder should be clearly marked as empty (MT) and returned to a storage area for pickup by the suppUo-. Empty and full cylinders should not be stored in the same place. 

He should know the number of rods, crossheaders, tubes and cooled test holes and be able to discuss int iM.igently any unusual or experimental on-reactor facilities. Design features with safety implications should be well understood e.g., front face check valves, cap detents, scram drive systems, coolant backup, etc. 

Not sure exactly what he should do, he muscles the container back onto the dolly and continues on. When Steve gets to the spot where he is to leave the cylinder, he notices that the protective valve cap is missing. 

Use a valve-cap retainer assembly that does not restrict vapor flow. This, and the following items, all add slightly to the cost of a tray. 

Change the valve tray decks to trays having dual light and heavy valve caps. This type of cap only permits the valve to open halfway at low vapor rates (see Fig. 8-10). 

Position discharge valve away from personnel and vent argon gas slowly to a well-ventilated outdoor location remote from personnel work areas and building air intakes. Return cylinders to the supplier with residual pressure, the cylinder valve tightly closed, and the valve caps in place. Allow liquid argon to evaporate in well-ventilated outdoor locations, which are remote from work areas and building air intakes. 

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