1、 ANSI/FCI 87-1-2017 AMERICAN NATIONAL STANDARDCLASSIFICATION AND OPERATING PRINCIPLES OF STEAM TRAPS Fluid Controls Institute, Inc. Sponsor: Fluid Controls Institute, Inc. 1300 Sumner Ave Cleveland, Ohio 44115-2851 iiANSI/FCI 87-1-2017 AMERICAN NATIONAL STANDARD Classification and Operating Principl
2、es of Steam Traps Sponsor Fluid Controls Institute, Inc. American National Standard American National Standard implies a consensus of those substantially concerned with its scope and provisions. An American National Standard is intended as a guide to aid the manufacturer, the consumer, and the gener
3、al public. The existence of an American National Standard does not in any respect preclude anyone, whether he has approved the standard or not, from manufacturing, marketing, purchasing or using products, processes, or procedures not conforming to the standard. American National Standards are subjec
4、t to periodic review and users are cautioned to obtain the latest editions. CAUTION NOTICE: This American National Standard may be revised or withdrawn at any time. The procedures of the American National Standards Institute require that action be taken to reaffirm, revise, or withdraw this standard
5、 no later than five years from the date of publication. Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute. Sponsored and published by: FLUID CONTROLS INSTITUTE, INC. 1300 Sumner Avenue Cleveland,
6、 OH 44115-2851 Phn: 216/241-7333 Fax: 216/241-0105 E-Mail: fcifluidcontrolsinstitute.org URL: www.fluidcontrolsinstitute.org Copyright 2017 by Fluid Controls Institute, Inc. All Rights Reserved No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise,
7、 without the prior written permission of the publisher. Suggestions for improvement of this standard will be welcome. They should be sent to the Fluid Controls Institute, Inc. Printed in the United States of America iiiForeword For many years, steam trap manufacturers and users have recognized the n
8、eed to establish standards for determining capacities of industrial steam traps. Many factors affect steam trap capacity and this has led to some confusion in the past. The FCI Steam Trap Section has developed a series of standards that serve as the authoritative source for reference regarding the c
9、apabilities of steam traps. Since steam traps are for the purpose of venting air and discharging condensate, many principles of operation are employed. This has led to some confusion in determining trap capacities. However, since all steam traps are governed by basic flow principles which will affec
10、t the amount of condensate through an orifice, a set of standards is very practical. In order to have a comprehensive standard, we have developed this standard, which describes the various types of steam traps, their principles of operation, and factors that affect their performance. This informatio
11、n enables a user to compare the relative capacities of traps of different types and different manufacturers. The Steam Trap Section of the Fluid Controls Institute began work on these standards many years ago. The final results represent the labors and the accumulated years of experience of many ind
12、ividuals in arriving at what we feel is a very complete and correct set of standards. At the same time, we as a committee realize that there are always opportunities to expand and to improve, and we invite comments for consideration. FCI recognizes the need to periodically review and update this sta
13、ndard. Suggestions for improvement should be forwarded to the Fluid Controls Institute, Inc., 1300 Sumner Avenue, Cleveland, Ohio, 44115-2851. All constructive suggestions for expansion and revision of this standard are welcome. The existence of a Fluid Controls Institute (FCI) standard does not in
14、any respect preclude any member or non-member from manufacturing or selling products not conforming to this standard nor is the FCI responsible for its use. Please go to the FCI web site for all of the latest technical articles and standards. ivCONTENTS PAGE Foreword iv 1. Scope . 1 2. Definitions 1
15、 3. Operating Principles . 1-3 4. Types of Steam Traps 4-7 5. Testing References .9 6. Metric Equivalent/Conversions .9 TABLES Table 1 Volume Change of 1 Lb. of Condensate Following Flow Through Orifice at Different Inlet Pressures and Temperatures 3 Table 2 Flow of Water Through Orifice of 1 Sq. In
16、.2Area at 100 PSI Differential Pressure 3 Table 3 Metric Equivalent/Conversions 10 FIGURES Figure 1 Orifice Area and Shape .2 Figure 2 Metal Expansion Traps 4 Figure 3 Bi-Metal Traps 5 Figure 4 Liquid Expansion Traps 5 Figure 5 Balanced Pressure Flexible Structure Traps 6 Figure 6 Upright Bucket Tra
17、ps 6 Figure 7 Inverted Bucket Traps .7 Figure 8 Float Traps .7 Figure 9 Non-Lever Free Float Traps 8 Figure 10 Thermodynamic Piston Traps8 Figure 11 Thermodynamic Disc Traps .9vANSI/FCI 87-1-2017 AMERICAN NATIONAL STANDARD Classification and Operating Principles of Steam Traps 1.0 SCOPE This standar
18、d is for the purpose of establishing and illustrating various classifications of Steam Traps in accordance with their basic principles of operation. This standard does not attempt to define details of conception or construction. 2.0 DEFINITIONS 2.1 Steam trap An integral, self actuated valve which a
19、utomatically vents air in the steam system and drains condensate from a steam containing enclosure while remaining tight to live steam. Most steam traps will also pass non-condensible gases while remaining tight to live steam. Note: Some designs will allow a minimal steam flow at a controlled or adj
20、usted rate using a separate secondary orifice. 2.2 Production tests - Tests carried out by the manufacturer to confirm that the steam trap functions correctly. These tests may be witnessed by the purchaser or his representative. In this case, these tests are referred to as witness tests. 2.3 Perform
21、ance characteristics - Carried out to determine the operational characteristics of a particular design of steam trap. 3.0 OPERATING PRINCIPLES 3.1 Factors Affecting Condensate Flow Through a Steam Trap One of the most common components to all steam traps is the discharge orifice. In some trap types,
22、 the valve seat and the discharge orifice are the same; in others, the discharge orifice may be smaller than the valve seat. 3.2 In considering steam trap capacities, therefore, it is important to explain what happens when fluid flows through an orifice. While in steam trapping we are concerned with
23、 the discharge of cold water, air and other gases, condensate and air mixtures, and hot (flashing) condensate, the main function of the trap is to discharge condensate, usually in the flashing state. The water discharge capacity of an orifice depends on the following factors: 1. The area and shape o
24、f the orifice and the coefficient of discharge CD 2. Lift of valve from orifice 3. The pressure drop across the orifice 4. Density of the water 5. The temperature of the water. 6. The physical changes that take place when water flows through the orifice. 3.2.1 Orifice Area and Shape Theoretically, t
25、he flow of cold water through a round, sharp-edged orifice in pounds per hour discharge is very nearly (psi)drop pressure x )(in area x 19,046Q 21=In other words, at 1 psi drop, a hole with an area of 1 in2 will pass 19,046 lbs/hr of cold water; at 4 psi drop the same 1 in2hole will pass 38,092 lbs/
26、hr. - or - Kg/hr = 5060 x area (cm2) x (bar) drop pressureIn other words, at 0.07 bar drop, a hole with an area of 6.45 cm2 will pass 8,635 Kg/hr of cold water; at 0.28 bar drop, 17,270 Kg/hr. In practice, however, the orifice creates friction, which reduces the flow. For example, the orifices shown
27、 in these sketches would pass 98%, 73%, and 52% (coefficient of discharge CD) of the theoretical flow, based on their flow entrance geometry. 98% 73% 52% Figure 1 1 23.2.2 Valve Lift The formula in paragraph 3.2.1 assumes a full open orifice. In a steam trap this is not necessarily true. The fact th
28、at, in some stream traps, the valve does not lift fully to the equivalent free area of the orifice does not imply poor design. It, however, makes comparison of steam trap capacities on orifice diameter alone unreliable. 3.2.3 Pressure Before and After the Orifice (Pressure Drop) The theoretical flow
29、 in 3.2.1 is based on the difference in pressure immediately before and immediately after the orifice, which is also called pressure drop. In a steam trap, the body and the mechanism of the trap offer resistance to flow, and the pipe connections on the discharge cause similar interference. So, in pr
30、actice, the pressures at the orifice proper are rarely, if ever, known and are variable, with a corresponding effect on discharge capacity. 3.2.4 Density of Water The density of water as compared to steam is another factor to consider. At typical atmospheric conditions, the density of water is 62.3
31、lbs/ft3and for steam it is .037 lbs/ft3. Therefore, 1 lb of steam at typical atmospheric conditions occupies a volume of approximately 1700 times that of water. 3.2.5 Temperature and Phase Changes Relative to Discharge Capacity Discharge capacity of condensate through a steam trap is most seriously
32、affected by the physical changes that take place. When discharging to atmospheric pressure, the physical state of water normally does not change as it flows through an orifice or a trap, provided the temperature is below 212F at the inlet. Condensate above 212F at the inlet, when reaching atmospheri
33、c pressure, cannot retain all of its heat and some of the heat causes “flash” steam to be generated. The result is a considerable increase in the specific volume and a corresponding reduction in the density of the mixture of steam and water flowing through the orifice. The theoretical effect of “fla
34、sh“ steam generation can be seen in Table 1, showing the volume of 1 lb. of condensate following release to atmosphere from various upstream pressures and temperatures. From Table 1, it can be seen that atmospherically discharged saturated condensate at 250F flashes and expands to 86 times its origi
35、nal volume at the inlet. At 300F it expands to 140 times, and at 350F it expands to 216 times its volume at the inlet. This considerable expansion of the condensate and flash steam mixture seriously interferes with the flow of condensate and reduces the discharge capacity. The impact of this reducti
36、on can be seen by comparing the theoretical flow of water through a one square inch area at various temperatures and at a pressure differential of 100 psi. (See Table 2). These figures clearly demonstrate how specific steam trap discharge capacity figures can be misunderstood unless the pressure and
37、 temperature of the condensate at the trap inlet and trap outlet are known.3 TABLE 1 VOLUME CHANGE OF 1 LB. OF CONDENSATE FOLLOWING FLOW THROUGH ORIFICE AT DIFFERENT INLET PRESSURES AND TEMPERATURES Upstream Inlet Downstream Outlet Expansion in outlet over inlet volumePressure (psig) Temperature (de
38、grees F) Volume (cu.ft./lb.) Pressure (psig) Temperature (degrees F) Volume (cu.ft./lb.) 0 60 0.016 0 60 0.016 0 times 0 212 0.0167 0 212 0.0167 0 times 15 250 0.017 0 212 1.48 86 times 52 300 0.0175 0 212 2.46 140 times 120 350 0.018 0 212 3.9 216 times Example: At 15 psig / 250 degrees F the conde
39、nsate has a volume of .017 cu.ft./lb. At atmospheric conditions this condensate has a volume of 1.48 cu.ft./lb., an increase of 86 times its volume under pressure. TABLE 2 FLOW OF WATER THROUGH ORIFICE OF 1 in2. AREA AT 100 PSI DIFFERENTIAL PRESSURE Temp. F F Below Saturation Flow lb/hr in2Cold Wate
40、r (60F) 278 190,460 308 30 107,000 318 20 90,000 328 10 70,000 333 5 47,000 4 3.2.6 Effect of Steam Trap Operating Principle A typical steam trap is not just a simple orifice but includes an integral, self-actuated valve operated either by temperature difference, buoyancy, or change of phase. This f
41、act must be taken into consideration when comparing steam trap capacity ratings. The capacity of all steam traps increases as the condensate temperature is lowered. Not all steam traps will, however, discharge condensate at steam temperature. Some traps, while being capable of operating at steam tem
42、perature, have their best condensate discharging characteristics at lower temperatures. It would, therefore, be impossible to fix an arbitrary standard temperature at which all steam traps should be tested. Thus, each manufacturer determines the best operating temperature range for their product, an
43、d the resultant capacity ratings are only meaningful when based on this stated operating temperature. For this reason, manufacturers who use this standard will state operating temperatures for each published trap capacity. 4.0 TYPES OF STEAM TRAPS 4.1 Principles of Operation While there are many way
44、s in which steam traps may be classified, it is probable that the basic principles of operation most simply satisfy our needs. The principles most commonly used in steam traps are as follows: Type 1 - THERMOSTATIC (Temperature). A thermostatic element, sensitive to the temperature difference between
45、 steam and cooled condensate, operates the valve. Type 2 - MECHANICAL (Buoyancy). The difference in density of steam and condensate operates a bucket or float controlled valve. Type 3 - THERMODYNAMIC (Change of Phase). The generation of flash steam (change from liquid to vapor phase) either throttle
46、s the discharge or operates a valve to regulate condensate flow. In the descriptions which follow, the order of presentation has no significance other than to simplify later explanation. This is particularly true in the case of air removal from the steam traps. 4.2 Thermostatic - (Temperature Operat
47、ed) Traps This general type of steam trap operates on the difference in the temperatures of the steam and the condensate reaching the trap. It follows that thermostatic traps discharge condensate at below the saturated temperature. It also follows that a mixture of air and gases and steam, which low
48、ers the mixture temperature, will also cause the trap to discharge. 4.2.1 Metal Expansion Traps A A. Construction Tube A has at its outlet a valve seat B and an inlet connection C for condensate. The metal rod D has a markedly greater coefficient of expansion than A, so that changes in temperature o
49、f fluid in the tube A causes the rod to expand or contract and so move the valve, plug E, to or from the orifice. The rod is threaded at F, allowing the adjustment position of the rod to suit operating conditions. B. Operation When cold, the rod D is contracted and the valve wide open. Air, forced out as steam enters the heating surface, flows through the orifice. Condensate follows and heats the rod D which expands, closing the valve. By adjustment of F, the trap can be set to discharge condensate at a predetermined temperature. Collection of a
