Steam trap

A steam trap is a type of pipe fittings designed for automatic removal of condensate of water vapor from steam condensate systems. Condensation in the systems appears as a result of the loss of energy by the steam in the heat exchangers or during starting heating of the heat pipes. The presence of condensate in steam piping systems leads to water hammer, a decrease in thermal power and a deterioration in steam quality. It is known that the use of steam traps in the equipment complex saves up to 20% of the useful energy of steam. To choose a steam trap, you need to know the conditions and operation mode of the heating network, the features of the equipment used and the characteristics of the steam traps themselves. Under the operating conditions of the heating system, we understand the fluctuations in the working pressure, as well as the back pressure on the steam traps themselves. In addition, the resistance of steam traps to corrosion, water hammer or freezing is sometimes required. It is also necessary to take into account the conditions for the release of air from the system when the thermal equipment is turned on. Consider the principle of operation of the three main types of steam traps.

Thermodynamic Steam trap, working principle:

Thermodynamic steam traps are the simplest and most common type of steam traps. Thermodynamic steam traps are designed for steam systems with low or medium condensate flow. The principle of operation of a thermodynamic steam trap is based on the difference in the passage of steam and condensate in the gap between the disk and the seat. When condensate passes through a steam trap due to its low speed, the disk rises and passes condensate. As steam passes through the steam trap, the speed increases, leading to a drop in static pressure, and the disk lowers onto the saddle. The steam above the disc, due to its larger contact area, keeps the disc in the closed position. As the steam condenses, the pressure above the disk drops, and the disk begins to rise again, letting in condensate. Periodically, steam traps discharge part of the steam, therefore, to avoid energy losses, manufacturers do not produce large-diameter thermodynamic steam traps.

Advantages of Thermodynamic Steam Traps:    

• Simple, reliable, compact design with low weight;
• Relatively low price of the device;
• Condensate is removed immediately when it enters the steam trap;
• Adjustment of the steam trap is not required;
• It is acceptable to use in systems with high (medium) pressure and with superheated steam;
• Do not collapse when freezing, do not freeze when installed in a vertical plane (Caution! Working in a vertical position can lead to rapid wear of the edges of the trap disc);
• Convenient in maintenance and repair;
• Insensitive to water hammer;
• Ability to determine normal operation by the frequency of disk impacts on the saddle;
• Great performance for its size;

Disadvantages of thermodynamic steam traps:

• Cycling leads to permanent loss of span steam;
• Unstable at low inlet pressure and high back pressure;
• There is a risk of locking the steam trap with air in the event of a sharp increase in pressure when starting the system (to solve this problem, it is recommended to use valves rather than ball valves for piping);
• When condensate is discharged into the atmosphere, a high level of noise is possible;

Thermostatic steam trap (capsule), working principle:

The principle of operation of the thermostatic steam trap is based on the temperature difference between steam and condensate. The thermostat is the sensitive element and actuator of the thermostatic steam trap. As a thermostat, bimetallic plates or capsules with a filler are used, which, when the temperature changes, deforms the inside of the capsule shape. The thermostat has a seat at the bottom that acts as a locking mechanism. When cold, there is a gap between the capsule disk and the seat allowing condensate, air and other non-condensable gases to escape from the steam trap. When heated, the thermostat lowers onto the saddle, preventing steam from escaping. A feature of thermostatic steam traps is the need for additional cooling of the condensate by several degrees relative to the condensation temperature in order to open the thermostat. Thus, this type of steam trap is more or less inertial. In addition to condensate drainage, this type of steam traps can also remove air and gases from the system, that is, it can be used as an air vent for steam systems. There are three modifications of thermostatic capsules that allow condensate to be removed at a temperature of 5 ° C, 10 ° C or 30 ° C below the vaporization temperature. This type of steam trap does not freeze if there is no rise in the condensate line behind it and the condensate will not flood it when the steam is turned off.

Advantages of thermostatic steam traps:

• Compact design, low weight, ease of maintenance;
• Continuous drainage of condensate and non-condensable gases;
• Reduced condensate temperature at the outlet of the device;
• Reduced pressure in the condensate line;
• Silent work;
• Great performance for its size;
• It is possible to install a steam trap in any position;
• Ability to use at high pressures;

Disadvantages of thermostatic steam traps:

• Upon failure, the saddle closes;
• Does not work with superheated steam;
• Sensitive to water hammer and sudden pressure fluctuations;
• Sensitive to defrost;
• The service life is lower than that of other types of steam traps;
• Inertia in work;
• Limitations on the ambient temperature - 25 ° C;
• Low resistance to pollution;

Float steam trap (mechanical), the principle of operation:

The principle of operation of float traps is based on the difference in the density of steam and condensate. The actuator is a ball float or a float in the form of an inverted glass. The float is connected to the exhaust valve through a lever. Condensate enters the body of the steam trap and, filling it, raises the float, while opening the exhaust valve. When the system starts up, air enters the steam trap, which is freely removed into the condensate line. Such steam traps provide continuous condensate drainage and are most suitable for systems with large heat exchange surfaces and the formation of large volumes of condensate.

Advantages of float traps:

• Stable operation at low loads;
• It is steady against sudden fluctuations of pressure;
• High productivity (up to 150 tons of condensate per hour!);
• Reliable in operation, resistant to water hammer;

Disadvantages of float traps:

• Low resistance to pollution;
• If the float breaks, the valve will be constantly closed, which can lead to rupture of the pipeline;
• Possible damage during freezing;

During operation, there must always be water (a water trap) in the body of the float trap. Loss of this water seal can result in unhindered steam escaping through the steam trap. This can happen with a sharp drop in vapor pressure and, as a consequence, boiling of condensate. To avoid this in systems where pressure fluctuations are possible, a check valve is installed in front of the steam trap. The float trap may be damaged by freezing. When installing the float trap in the open air, it is necessary to use the thermal insulation of its body.