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How to choose steam trap correctly

The steam trap is an automatic valve used on steam heating equipment, steam transmission pipelines and steam utilization devices. The condensed water generated after the steam does work is quickly discharged from the device, and the fresh steam is prevented from leaking, and the efficiency of the device is kept at the best state.

No steam trap of any form or kind is a panacea. In order to select and install an ideal steam trap, the structure and type of steam-using equipment, the conditions and purpose of use, and the supporting airtightness of the equipment should be considered. The following mainly explains the key points of selection from the perspective of steam traps.

(1) Terminology of steam traps

Since steam traps have many differences from general valves in terms of structure and performance parameters, especially some special terms are easy to confuse, in order to make the selectors understand steam traps more clearly and choose them correctly, some main terms are listed below Terminology explained.


Mechanical Steam Traps: Steam traps that are actuated by changes in condensate temperature.

Thermostatic Steam Traps: Steam traps driven by changes in condensation temperature.

Thermodynamic Steam Water Valve: A steam trap driven by the dynamic characteristics of steam and condensate.

Maximum Allowable Pressure: At a given temperature, the highest pressure that a steam trap can withstand for a sustained period of overdispensing.

Maximum working pressure: Under correct operating conditions, the maximum pressure at the inlet end of the steam trap is given by the manufacturer.

Operating Back Pressure: Under operating conditions, the pressure at the outlet of the steam trap.

Back pressure ratio: The percentage of working back pressure and working pressure.

Maximum Allowable Temperature: The highest temperature that the steam trap housing can withstand for a long time at a given pressure.

Subcooling: The absolute value of the difference between the condensed water temperature and the saturation temperature at the corresponding pressure.

Condensate water discharge capacity: Under the condition of given pressure difference and 20℃, the maximum weight of condensate water that can be discharged by the steam trap within 1 hour.

Thermal condensate displacement: Under a given pressure difference and temperature, the steam trap can discharge the maximum weight of thermal condensate within 1 hour.

Steam leakage: the amount of fresh steam leaked from the steam trap per unit time.

No-load steam leakage: the steam leakage of the steam trap under the condition of fully saturated steam.

Steam leakage rate with load: The steam leakage rate of the steam trap under a given load rate.

No-load steam leakage rate: the percentage of no-load steam leakage to the maximum thermal condensate displacement under the corresponding pressure.

Steam leakage rate with load: the percentage of steam leakage with load to the actual thermal condensate discharge during the test period.

Load rate: the percentage of the actual thermal condensate discharge during the test period to the maximum thermal condensate discharge under the test pressure.

(2) Capacity and safety rate of steam trap

When selecting a steam trap, it is necessary to fully understand the form, purpose, and characteristics of steam-using equipment such as steam pipes and various heat exchangers to be used, and to accurately grasp the capacity of the equipment itself. This is a prerequisite. If the capacity of the steam-using equipment is known, the capacity of the steam trap it uses can also be determined. To determine the capacity of the steam trap, it must be obtained according to the following principles:

Capacity of steam using equipment (condensed water generation) × safety rate = capacity of steam trap.

Safety rate, that is, when determining the capacity of the steam trap, the estimated safety factor can ensure that the steam trap can work normally even if there is an error between the actual condensed water production of the steam using equipment and the marked capacity. This safety rate is neither stipulated purely in theory and cannot be obtained through calculation; nor is it completely derived from empirical data. Generally speaking, the best way to consider the safety rate is to ask the trap manufacturer directly. If the safety rate of the steam trap is not selected properly, the capacity of the steam trap will be too large or insufficient, which will have extremely bad consequences.

If the safety rate is too large, that is, when a steam trap with too large capacity is installed and used, the following disadvantages will occur:

The large capacity of the steam trap increases the cost.

If it is a steam trap with intermittent action, too large capacity will lengthen the action cycle of the trap, increase the average retention of condensed water, and reduce the capacity of steam-using equipment.

For steam traps that operate continuously (proportionally) like float traps, due to the small opening of the disc, excessive capacity will cause roughening of the valve seat (when high-speed fluid passes through a narrow gap, the contact surface will Corrosion, forming grooves), damage the valve seat and cause leakage.

Shorten the life of the steam trap.

On the contrary, if the safety ratio is too small, the capacity of the steam trap used will be too small, and the following failures will occur:

It cannot adapt to the load change of the steam using equipment, so that the operating efficiency is significantly reduced.

Condensate passing through traps often reaches maximum levels, leaving the disc and seat susceptible to corrosive damage.

Shorten the life of the steam trap.

Therefore, when selecting a steam trap, not only must the type and capacity of the trap be fully studied in many aspects, but also the guidance of the steam trap manufacturer must be accepted.

(3) Selection of steam traps

When selecting a steam trap, the shortest form must be selected according to the type and conditions of use of the steam device. For this reason, it is necessary to correctly grasp the characteristics and operating conditions of the steam using device. When determining the type of steam trap, the following items must be understood in detail in order to select a steam trap that meets the requirements of use.

The condensate load of the steam using device and the load characteristics of the condensate.

Steam conditions: pressure, temperature, saturated steam or superheated steam.

Back pressure condition: discharge or recover condensed water to the atmosphere (what is the back pressure).

Body material.

Connection Type.

safety rate.

Others: the corrosiveness of condensed water; the possibility of water hammer; whether it will freeze; whether there are clear requirements for noise and environmental pollution; the difficulty of maintenance and inspection, etc.

In addition, when selecting steam traps, attention should be paid to the selection conditions of steam traps, namely:

Select the type that meets the conditions of use.

Choose the capacity that suits the conditions of use.

Choose good durability that has the required conditions of use.

Choose products that are easy to repair.

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