steam trrap working principle

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simple techniques for surveying steam traps

Costs of energy and steam have fluc-tuated significantly in recent years.When these costs were low, eco-nomic analysis did not justify repair of steam leaks from gaskets, holes,valves or steam traps. Later, whensteam costs escalated dramatically,economics favored the quick repair of these same leak sources. While steamcosts vary from time to time, the needto survey for leaks and perform repairsnever lessens.

While the value of steam can be a

basis for decision making regardingthe repair of leaks, it is not the onlyreason. Other values need to be con-sidered: cost and availability of wa-ter, cost of handling, pumping andtreating water, and production itself.

Production is why the plant is inbusiness, and this alone should jus-tify steam trap surveys. Not only areleaks a consideration, but so are trapsthat are backing up condensate andcausing lost production. This cost isanother major consideration.

When condensate is not being

drained, bypass or drain valves areopened to solve the problem. By-

passes discharging into closed re-turns are not readily seen, but bothapproaches to solving the back upproblem can be result in lost energy.

When discharging into the closedreturn line, these pressures can be-come unexpectedly high. The highreturn pressure can inhibit drainage

Fig. 1—Ruptured tracing is a typical and costlysteam loss.

Fig. 2—Defective gasket of this trap permits lossof live steam from the system.

Fig. 3—Open end of tracing not only loses steambut can also create other maintenance problemssuch as the corrosion of concrete sill shown here

© 1995 Yarway Corporation

from other equipment, as well as pro-ducing additional steam trapping

problems. The survey, locating both failed

open and failed closed traps, is usu-ally justified on the basis of energysavings alone.

Considering only steam cost, TableI shows the value of leakage for vari-ous sizes of leaks. The assumed con-ditions are steam at 100 psi, discharg-ing to atmosphere with an assumedvalue of $5.00 per 1,000 pounds of steam.

The losses for 100 psi shown in Table I are 2.75 times greater for

steam generated at 300 psi; 5.35times greater with 600 psi steam.

There has not been any attempt to fig-ure cost of the additional make-up water, water treatment chemicalsinto these costs.

This awareness of the seriousnessof steam leaks leads first to the ques-tion of where those leaks can be ex-pected in a typical plant. Usually theyexist in open bypasses; defectivevalves (or those left in a “cracked

SteamLeak Wasted Cost

Diameter Per Month Per

(in.) (lb.) Year

1/16 13,300 $ 7981/8 52,200 3,1321/4 209,000 12,540

1/2 833,000 49,980

(Steam 100 psi; at $5.00 per 1000 lb. dis-charging to atmosphere)

Table I—Cost of Steam Leak(Open Bypass, Defective Valve or Trap)

open” position merely for visual indi-cation of system operation); rupturedand open steam tracing; and in de-fective steam traps. In one refinerythat had never inspected their traps,a steam trap survey revealed that 34%of the traps examined had failed—most in the open position.



The Steam Trap Survey The steam trap survey is a plannedexamination of a number of traps withthe methodical cataloging of the es-sential data pertaining to each—typeand size, steam pressure at trap in-let, temperature at inlet and outlet,and operating condition.

If the plant or steam system is exten-sive, the survey need not include all

the traps on the first pass. In fact, it ispreferable to survey a big plant bysection, system or process unit. Bytaking this approach, the work can bedone more thoroughly. For example,traps hidden by fittings, other equip-ment, or covered by insulation can belocated. And of equal importance,each trap can be tagged.

Traps are tagged in order to iden-tify their location and facilitate recordkeeping and reporting. The tags canbe made of aluminum, stainless steelor plastic by a hand operated print-ing tool as the surveyors move downthe system. Tagging can go accord-ing to a fairly standard coding. Forinstance, “T-1” would be the tag forthe first trap on a tracing line; “D-3”would be the third drip trap in a pip-ing system. Other designations wouldbe “P-” for process, “H-” for heating,“MB-” for meter box. Or a differentcoding system could be developed tosuit the requirements of a certainplant.

Fig. 4—To determine trap performance by visual observation of condensate discharge, you should know the difference between flash steam(lazy vapor discharging with condensate—left) and live steam (high temperature, high velocity discharge—right).

The trap survey will reveal varioustypes of steam losses—like open trac-ing and bad valves. But it’s main pur-pose is the checking of trap perfor-mance. There are various methods fortrap checking: (1) visual observation,(2) by sound, and (3) by temperaturemeasurements.

None of the checking methods pro-vide a “cure-all” for all trap trouble-

shooting situations. The best resultscan be achieved by using a combina-tion of checking methods or by usingone method to cross-check indica-tions provided by another. Always usemore than one method.

Visual Method Visual observation of condensate dis-charging from the trap is the easiest,and perhaps the best way to check its performance. No special equip-ment is needed, but you should knowthe difference between flash conden-

sate and live steam. Figure 4 illustratesthe difference between condensateand steam.

Flash condensate is the vapor thatforms when hot condensate is dis-charged to the atmosphere. The pres-ence of flash is natural and does notimply waste steam or trap failure.

If the trap does not discharge to theatmosphere but into a closed conden-sate return system, a test valve should

be installed downstream of the trapWhen it is desired to check trap per-formance by observation, the isolationvalve is closed to shut off the conden-sate return line, and the test valve isopened to the atmosphere. If flash andcondensate discharge to the atmo-sphere as the trap cycles a few timesthe trap is operating properly.

But suppose the steam that ac-

companies the condensate is notflash but is live steam discharging hot,at high velocity (and, in the case of adisc trap, with a rapid chattering inexcess of 60 times per minute). Thenyou can assume the trap has failed.

Sound MethodBy carefully listening to them operatetraps can be checked without visuaobservation of the condensate dis-charged. This method is more con-venient when working with closedcondensate return system. The nec-

essary equipment consists of an in-dustrial stethoscope, or a homemadelistening device such as a two-footlength of 3/16" steel rod in a filehandle, a piece of wood dowel, or ascrewdriver.

With practice, the operation of thetrap can be heard with any of thesehomemade devices by placing oneend of the tool against the trap bon-net and the other end to your ear.



Temperature Measurements A steam trap is essentially an auto-matic condensate valve, the onlyfunction of which is to pass conden-sate and hold back steam. This defini-tion implies the presence of liquidcondensate-water. Trap operation,therefore, can be checked by makingtemperature measurements on thepipeline about 12 inches upstream

and downstream of the trap. Two requirements for this method

are a simple contact pyrometer formaking the measurements on the sur-face of the pipe, and a knowledge of line pressure upstream and down-stream of the trap. For each steampressure there is a correspondingsteam temperature. Table II showstypical pipe surface temperature read-ings corresponding with several op-erating pressures.

Let’s assume the upstream pres-sure in the piping system is 150 psigand the pressure downstream of thetrap is 15 psig. An upstream tempera-ture measurement with the pyrometer is335F and a downstream reading is225F. File or wire brush the pipes atpoints of measurement to providegood contacts for the tip of the py-rometer.

Table II shows that for an upstreampressure of 150 psig, a pyrometerreading between 348F and 329Fshould be obtained. And for a down-

stream pressure of 15 psig, a pyrom-eter reading of between 238F and225F is desirable. We can conclude,therefore, that the trap is operatingproperly.

Now let’s assume the same pres-sures, but a pyrometer reading of 335F upstream and 300F down-stream of the trap. The elevateddownstream temperature is greaterthan expected for a 15 psi return line.

The high temperature suggests highpressure and this may be due to a

blowing trap. Use another checkingmethod to verify before repairing.

In still another example, supposethe pyrometer readings are 210F on both sides of the trap. That’s okaydownstream where we know pressureis 15 psig. But it’s too low for a read-ing upstream where we know we have150 psig in the line. There is probablya restriction in the line that is reduc-ing the pressure to the trap. A cloggedstrainer may be the culprit, so blow itdown before looking any further forthe problem.

Although the foregoing examplesdeal with a closed return system, the

temperature measurement methodcan also be used to check traps dis-charging to the atmosphere. In thissituation, of course, the downstreampressure is always atmospheric.

Review Application BasicsOccasionally, a trap will be found tobe fully operable after a performancecheck by one of the above methodshas led to it’s being pulled out of the

Pipe SurfaceSteam Steam Temperature

Pressure Temperature Range(psig) (F) (F)

15 250 238-22550 298 283-268100 338 321-304150 366 348-329200 388 369-349450 460 437-414

Table II—Pipe Surface Tem-perature vs. Steam Pressures

Fig. 5—Determining trap performance by the sound method is difficult where manytraps discharge in close proximity. Temperature measurement method is preferable.

line. In such a situation, misapplica-tion should be considered as the

cause of nonperformance rather thantrap failure. Here is what to look for ifmisapplication is suspected:

1. Oversizing—probably the mostcommon type of misapplication

The trap simply has too much ca-pacity for the situation. Try a smallercapacity trap.

2. Freeze-Proof Installation—thermo-static and thermodynamic (disc)traps can be installed to provideself-drainage, thus making the in-stallation freeze-proof in cold

weather. The freeze-proof methodfor installing a Yarway disc trap, forinstance, is in vertical piping dis-charging down. If the trap must beinstalled horizontally, it’s bonnetshould be on the side. Read theprinted instructions packed withthe trap. Use a vacuum breaker toassure gravity flow.

Trap Operating Properly Failure

Disc (impulse Opening and snap closing of Normally fails open. Cycles inor thermodynamic) disc excess of 60 per minute.

Mechanical Cycling sound of bucket as Fails open—sound of steam(bucket) it opens and closes blowing through.

Fails closed—no sound.

Thermostatic Sound of periodic discharge if Fails open—sound of steam(bellows) on medium to high load; possibly blowing through.

no sound if light load, throttleddischarge. Fails closed—no sound.

Table III—Typical Operating Sounds of Various Types of Traps



Yarway Corporat ion • 480 Norr istown Road • P.O. Box 350 • B lue Bell , PA 19422Phone 610-825-2100 • Fax 610-825-1235 • www.yarway.com

North American Regional Offices: Eastern 800-523-6248 • Southeast 800-561-5816Southwest 800-561-5819 • Midwest 800-561-5814 • Western 800-561-5813

Inquiries from other than North American Locations should be addressed to the Inter national Department, Blue Bell, PA

3. Proper Direction Flow —althoughit may sound obvious, the fact isthat a trap is occasionally installed

backward, with its upstream or in-let side connected into the down-stream piping. Look for the arrowor “inlet”/”outlet” markings on thetrap and install it in the line prop-erly.

4. Trap Location—condensate dis-charge piping should be connectedto equipment at its low point to pre-vent accumulation or pockets of condensate and blanketing theheating surfaces. Pitch the pipingtoward the trap to minimize waterhammer.

5. Gravity Flow to Trap—a good pitchof the inlet piping to the trap helpscondensate flow toward the trap,displacing steam which otherwisecould cause steam binding of thetrap.

6. Short Drainage Legs—these alsominimize the tendency for freezeupin cold weather.

Fig. 6—This operator is using a contact pyrometer to make upstreamand downstream temperature measurements to determine trap perform-ance in a closed condensate return system.

7. Trap Each Unit In-dividually —if youtry to drain morethan one piece of equipment withone trap, short cir-cuiting is very likelyto occur due to dif-ferences in pres-sure drops. The

unit with the leastpressure drop willblanket or shortcircuit the othersand cause unevenand inefficientheating.

8. Size Each TrapSeparately —con-densate loads vary

from one piece of equipment to an-other. So you can’t expect one trapto perform equally well in all cases.

Higher capacity traps are requiredfor heavier condensate loads.

What Kind of Savings fromTrap Survey?If your steam system is extensiveenough to include more than 500traps, a steam trap survey will prob-ably uncover some significant steamlosses. Take the remedial actions in-dicated by the survey, and savings insteam should be apparent. For in-stance, in the refinery mentioned at thebeginning of this article, a 3/4-inch

trap failed open was found to be wast-ing about $160 per month in gener-ated steam. Multiplied by the numberof defective traps (34% of those sur-veyed) approximately $70,000 per month in steam was being lost.

In a midwestern chemical plant, atrap survey resulted in a steam sav-ing of 20,000 lb/hr (cost of steam atplant unavailable). In a midwesternrefinery that included its cost of steamfactor, $3,000 per month savingswere reported.

A steam trap survey will uncoversignificant problems with regard to thesteam and condensate systems. This isespecially true if your systems havenot had any attention for a period oftime. The benefits of a system surveyand repair include improved produc-tion, improved condensate collectionand energy savings.

If we assume some typical or aver-

age conditions, we can estimate thepotential energy savings based onthe leaks (gaskets, pinched tubes, etc.),leaking valves (isolation and bypass)and steam traps for an installed trappopulation of 150.

Leak Source # of Leaks lb/hr $/day (4)

Leak (1) 5 --- 12.50 Valves (2) 2 260 62.40 Traps (3) 20 34 81.60

TOTAL 156.50= $40,690/year (5 days/week, 52 weeks)

(1) Surveys show that leaks are 3%of the installed trap populationLength of leak is assumed to be 4ft. at 100 psi and $2.50/day.

(2) Surveys show that valve leaks are1% of the trap population. As-sumed average operating pres-sure is 300 psi.

(3) Surveys show that in systemswithout a maintenance program20% of the installed traps can beleaking. There is no accounting forthe cold and plugged strainer andorifice drainers.

(4) Steam cost assumed at $5.00/1000 lb.

This potential reduction in operatingcosts, combined with the improve-ment in operation, makes the surveyan attractive proposition.

231 Rev. 7/95 10M 998Q Printed in U.S.A .

steam trrap working principle

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