Thermostatic traps

Thermostatic traps are temperature-sensitive traps there are several basic types. They respond to either a temperature difference between the steam and the condensate or directly to a temperature of either steam or condensate. All thermostatic traps are operated and controlled by the temperature in the line upstream of the trap time Is necessary for the operating elements to either absorb heat to cause the valve to close or dissipate heat to cause the valve to open. They usually discharge condensate below the steam temperature and require a collecting leg before the trap to permit some subcooling of condensate. Therefore, sufficient piping length should be provided at the trap inlet to prevent the condensate backup from interfering with the heat transfer surface. 

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This makes the thermostatic trap suitable to remove large quantities of air and cold condensate at the start-up condition, especially for batch-wise processes. 

Like the inverted-bucket trap, float-and-thermostatic traps as a group handle a wide range of steam pressures and condensate loads. However, each individual trap has a very narrow range of pressures and capacities. This makes... 

The key advantage of float-and-thermostatic traps is their ability for quick steam-system startup because they continuously purge the system of air and other noncondensable gases. One disadvantage is the sensitivity of the float ball to damage by hydraulic hammer. 

Float-and-thermostatic traps are an economical solution for lighter condensate loads and lower pressures. However, when the pressure and capacity requirements increase, the physical size of the unit Increases and its cost rises. It also becomes more difficult to handle. 

Thermostatic traps are compact, and a given trap operates over a wide range of pressures and capacities. However, they are not recommended for condensate loads over 15,000 pounds per hour. 

Steam trap. The steam trap must be adequately sized to avoid backup. Also, a trap with minimum holdup of condensate is preferable. If the steam fails, condensate will re-evaporate and return to the tubes, so an absolute minimum condensate volume in the trap is desirable. Thermostatic traps have proven satisfactory for many applications. 

Effects of Water Hammer. Water hammer has a tremendous and dangerous force that can collapse floats and thermostatic elements, overstress gauges, bend mechanisms, crack trap bodies, rupture fittings and heat exchange equipment, and even expand piping. Over a period of time, this repeated stress on the pipe will weaken it to the point of rupture. 

It is clear that in most cases other than very large distribution mains, in TD traps are sufficiently large. With shorter distances between drain points, or smaller diameters, then i in low-capacity traps more than meet even start-up loads. On very large pipes it may be worth fitting I in traps, or two in traps in parallel. Low-pressure mains often are drained through float/thermostatic steam traps, and these traps are now available for use at much higher pressures than formerly, where it is known that waterhammer will not be present. 

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 groupings then may be described as mechanical, which will include both ball float and inverted bucket steam traps thermostatic, which will include both balanced pressure and bimetallic elements and thermodynamic or disc pattern traps (Figure 22.13). Each type of trap has its own characteristics, and these will make one pattern of trap more suitable for use on a given application than another. In practice, it is usual to find that the applications in any given plant fall into a small number of categories, and it often is possible to standardize on a quite small number of trap types. 

In a similar way, many small jacketed pans, steam radiators and convectors, and some steam tracer lines can operate most economically if the condensate is retained within the steam space until it has sub-cooled a little, making thermostatic pattern traps the most suitable for these... 

Thermostatic steam traps contain a bellows-type element that expands in contact with steam, causing the valve to close, but opens at lower temperatures to allow condensate or air to escape. Typically, thermostatic steam traps are used at up to 150 to 250 psig. 

Float thermostatic steam traps employ a float valve that rises in the presence of condensate and then opens to permit the discharge of the condensate. 

The thermostatic element component only opens if the surrounding temperature is lowered by the presence of air or other noncondensable gases. These gases can then escape, but entering steam again closes the thermostatic valve. Float thermostatic steam traps are typically used at up to 125 psig. 

Fig.4.3. Experimental arrangement for investigation of pyrolysis of molecules by the method of semiconductor sensors 1 - reaction vessel, 2 - quartz slab with a ZnO film (sensor), 3 - filter, 4 - contacts, 5 - incandescent filament, 6 - thermocouple, 7 - cell with a substance, 8 - lamp - manometer, 9 - pin, 10 - flask, 11 - sealing bulkhead, 12 - trap, 13 - thermostat.

Procedure. Finely powdered antimony trifluoride is placed in the reservoir of the feed. Phosphorus oxychloride and then antimony pentachloride are placed in the reaction vessel. The temperature of the bath is maintained, thermostatically, at 75° and the pressure kept at 190-200 mm., and the antimony trifluoride is then added slowly from the feed. The distillates in the traps are united and fractionated. The distillate, up to b.p. 90°/760 mm., is collected and carefully refractionated, giving pure phosphorus oxydichlorofluoride, b.p. 54° (20 per cent yield). 

Fig. 22. Thermobalance for vapor pressure measurements. Schematic drawing of experimental equipment. A-Knudsen cell B-cold trap C-Ionization gauge D-Balance and housing E-Diffusion pumps F-Thermostatically controlled reaction chamber...

The apparatus and the special accessories necessary for this work are schematically illustrated in the Fig. 22. The reaction chamber used for the Knudsen effusion method is positioned above the balance. The reaction chamber is thermostatically controlled and connected with a cold trap. Both of them are protected from outside temperature effects by an insulating material. This protection leads to a more constant temperature and a straight line in the recorded loss in weight. 

Fig. 10. LS photometer60 for use at = 1086 nm A - laser, B - lens, C - shutter, D -rotating chopper, E - shutter, F - entrance window, G - thermostat vessel, H - metal shield, I - shutter, J - thermostat liquid, K - cylindrical LS cuvette, L - light trap, M - shutter,...

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