FAQ

1. Since the drainage capacity of a steam trap is measured under conditions of continuous drainage, but virtually all steam traps do not drain continuously in actual operation—instead, they typically drain intermittently—it is essential to take into account the downtime during actual operation.
2. Even when the capacity of a steam-using piece of equipment has been determined, that capacity refers only to the load under normal operating conditions. When the equipment begins operation (at startup)—during what is known as the “warm-up phase”—both the equipment itself and the material being heated are at room temperature, resulting in a significant increase in steam consumption. In other words, steam-using equipment often generates a large amount of condensate during the warm-up phase.

For these two reasons, when selecting a steam trap, the trap’s discharge capacity should be multiplied by a safety factor.

There are many factors to consider when selecting the right steam trap, but the main ones are as follows:

1. Select the appropriate type of steam trap based on the specific application;
2. Select the appropriate connection size based on actual operating conditions;
3. Select a steam trap with the appropriate pressure and temperature ratings based on the actual operating conditions;
4. Based on the amount of condensate that may be generated by the steam heating equipment during normal operation, multiply this figure by a selection factor of 2 to 4, and then select a steam trap based on its actual drainage capacity.

In the phase transition of water, a system in which water and water vapor coexist in equilibrium is called saturated. This saturated state has a critical point; the temperature at this critical point is called the critical temperature, which is 374.15 °C.

The pressure at the critical point is called the critical pressure, which is 22.12 MPa.

The steam leakage rate of a steam trap is classified into two categories: under-load steam leakage rate and no-load steam leakage rate.

Steaming rate under load:

The steam leakage rate under load is defined as the percentage of steam leakage under load relative to the actual amount of hot condensate discharged during the test period.

No-load steam leakage rate:

The no-load steam leakage rate is defined as the percentage of the no-load steam leakage relative to the maximum hot condensate discharge at the corresponding pressure.

Since the primary function of a steam trap is to promptly discharge condensate from steam-heated equipment or steam piping systems while preventing steam leakage, thereby improving the efficiency of steam-using equipment and achieving energy savings, the key indicators for evaluating the performance of a steam trap should be its drainage performance and steam retention performance. Based on the definition of steam leakage rate, the magnitude of a steam trap’s steam leakage rate comprehensively reflects the quality of its drainage and steam retention performance.

A steam trap is a valve that automatically removes condensate from steam lines and steam-using equipment and prevents steam leaks.

There are nine performance metrics for steam traps: body strength, operational performance, minimum operating pressure, maximum operating pressure, maximum backpressure ratio, steam leakage rate, air venting capacity, discharge temperature, and discharge volume.

Because the contact area between the valve body and the plug of a plug valve is very large, rotating the plug generates significant torque. In this case, surface corrosion can quickly cause the sealing element to lose its seal, and increase the torque required to operate the plug valve.

Steel and cast iron plug valves used with corrosive media should be coated with phenolic resin or other plastic coatings.

National Standard GB/T 12237, “Steel Ball Valves for the Petroleum, Petrochemical, and Related Industries,” stipulates that the ball valve stem shall be designed such that, under the pressure of the medium, the stem will not be forced out of the valve body even when the stem packing is removed (e.g., when the packing gland is removed).

Single-Seal Butterfly Valves

In a unidirectional sealed butterfly valve, the disc must face the direction of media flow when closed; the media flows in only one direction, and the valve body must be marked with an arrow indicating the direction of media flow. Care must be taken to ensure the media flows in the correct direction during installation.

Double-Seal Butterfly Valves

A bidirectional butterfly valve allows the disc to face either toward or away from the direction of media flow. During installation, there is no need to consider the direction of media flow, and there are no arrows on the valve body indicating the flow direction. The load on the stem of a bidirectional butterfly valve is greater than that of a unidirectional butterfly valve. In design, for butterfly valves of the same diameter and pressure rating, the stem diameter of a bidirectional butterfly valve is larger than that of a unidirectional butterfly valve.

The horizontal projection of the pivot pin axis of a swing check valve is perpendicular to the axis of the valve body’s flow passage and forms an angle with the sealing surface.

In a standard globe valve, the medium flows in from below the disc and out from above the disc. If the globe valve has a double disc, the medium flows in from above the disc and out from below the disc. Globe valves with a DN greater than 250 mm allow the medium to flow in from above the disc.

When conducting performance tests on steel gate valves, care must be taken to ensure that no external forces are applied to either end of the valve that could affect leakage at the sealing surfaces.

National Standard GB/T 12234, “Steel Gate Valves with Bolted Covers for the Oil and Gas Industry”, stipulates that the valve stem nut shall be installed from the top of the bracket, and the upper part of the gate valve stem nut shall be a polygonal cylinder with a keyway or a structure of equivalent strength connected to the handwheel. When the valve is open, the handwheel shall be removable without causing the valve stem and gate to drop to the closed position. If a threaded bearing gland is used, it shall be secured by spot welding or other methods.

Double-sided forced sealing in gate valves:

This means that the gate and the seat sealing surfaces are sealed at both the inlet and outlet ends of the valve. The seal is maintained by the axial force of the valve stem. When no medium is present, the normal force between the sealing surfaces must not be less than the sum of the static pressure of the medium and the sealing force.

Single-sided positive sealing in gate valves:

This means that there is no seal between the gate and the seat sealing surface at the medium inlet; in this area, there is either no contact pressure at all, or the contact pressure is less than the sealing contact pressure. On the medium outlet side, the seal between the gate and the seat sealing surface is forcibly maintained by the axial force of the valve stem and the medium pressure. When there is no medium present, the contact pressure on the sealing surface must not be less than the sealing contact pressure.

Ⅰ.Classified into two categories based on gate plate construction

1. A parallel-type gate valve is a gate valve in which the sealing surfaces are parallel to the vertical centerline, meaning the two sealing surfaces are parallel to each other. Parallel-type gate valves are further classified into double-disc and single-disc types. They are also categorized as having or not having a flow-through orifice.
2. A wedge gate valve is a type of gate valve in which the sealing surfaces are set at an angle to the vertical centerline, forming a wedge shape. Wedge gate valves are further classified into double-disc, single-disc, and elastic-disc types.

Ⅱ.Classified into two categories based on the construction of the valve stem

1. A rising-stem gate valve is a type of gate valve in which the stem nut is located on the bonnet or bracket, and the stem is raised or lowered by rotating the stem nut to open or close the gate.
2. A concealed-stem gate valve is a type of gate valve in which the valve stem nut comes into direct contact with the medium inside the valve body, and the gate is opened and closed by rotating the valve stem.

The minimum stem diameter refers to the diameter of the portion of the stem that comes into contact with the packing. The minimum stem diameter refers to the diameter of the undercut on the stem threads.

The paint on the handles and handwheels corresponds to the paint colors of the sealing surface materials; see the table below for details.

Paint colors for valve handles and handwheels:

The standard opening and closing directions for general-purpose valves are as follows: clockwise is closed, and counterclockwise is open.

The mandatory and optional markings for general-purpose valves are shown in the table below.

Valve markings:

Note: The nominal pressure value stamped on the valve body is equal to 10 times the MPa value; when this value is located below the nominal pressure value, it is not preceded by the prefix “PN”.

Marking method:

(1) Markings for valves with a nominal size of DN50 or greater:

1. Items 1 through 4 in the table are mandatory markings and must be affixed to the valve body.
2. Items 5 and 6 in the table are mandatory markings only when required by a specific valve standard; they should be marked on the valve body and flange, respectively.
3. Unless otherwise specified in the relevant valve standards, items 7 through 19 in the table are markings to be used as needed. When required, they may be marked on the valve body or on a nameplate.

(2) Markings for valves with a nominal size less than DN50:

1. Items 1 through 4 in the table are mandatory markings. Whether these markings appear on the valve body or on a label is determined by the product designer.
2. The markings for items 5 through 19 in the table shall comply with the requirements for markings 2 and 3 for nominal sizes greater than or equal to DN50.

(3) Additional symbols:

1. Any marking in the table may be applied at different locations. For example, any marking placed on the valve body may also be repeated on a label.
2. As long as the additional mark does not cause confusion with the marks in the table, any other mark may be added. For example: product model numbers, etc.

For pressure-reducing valves, in addition to the 19 markings required for general-purpose valves, the valve body must also bear the following: date of manufacture, applicable medium, and outlet pressure.

In accordance with the provisions of GB/T 12250-2005, markings for steam traps may be affixed to the valve body or to a nameplate.

The marking of safety valves shall comply with the provisions of GB/T 12241-2005.

Ball valves, parallel-type gate valves, and plug valves are marked in accordance with API 6D-2014.

The material code for sealing surfaces machined directly from the valve body is denoted by “W”; see the table below for the codes of other materials.

Designation for valve seat sealing surface or lining material:

Note: When the sealing surfaces of a sealing pair are made of different materials, the material with the lower hardness is used to denote the pair.

For gate valves, globe valves, check valves, ball valves, and butterfly valves, the sealing pressure qMF must be less than the sealing pressure q, and the sealing pressure must be less than the allowable sealing pressure [q] (i.e., qMF < q < [q]).