Industrial Machinery Repair Part Episode 2 Part 9 pptx

Steam Traps 437Figure 22.5 Thermostatic trap the condensate.. Condensate load greater than design •High-pressure traps discharge into low-pressure return • Internal parts of trap broken

434 Steam Traps

Figure 22.2 Float-and-thermostatic trap

it critical to select a trap that can handle the specific pressure, capacity, andsize requirements of the system

The key advantage of float-and-thermostatic traps is their ability for quicksteam-system startup because they continuously purge the system of air andother noncondensable gases One disadvantage is the sensitivity of the floatball to damage by hydraulic hammer

Float-and-thermostatic traps are an economical solution for lighter sate loads and lower pressures However, when the pressure and capacityrequirements increase, the physical size of the unit increases and its costrises It also becomes more difficult to handle

conden-Thermodynamic or Disk-Type

Thermodynamic, or disk-type, steam traps use a flat disk that moves between

a cap and seat (see Figure 22.3) Upon startup, condensate flow raises thedisk and opens the discharge port Steam, or very hot condensate enteringthe trap, seats the disk It remains seated, closing the discharge port, aslong as pressure is maintained above it Heat radiates out through the cap,thus diminishing the pressure over the disk, opening the trap to dischargecondensate

Steam Traps 435

Cap

Disk

Figure 22.3 Thermodynamic steam trap

Wear and dirt are particular problems with a disk-type trap Because of thelarge, flat seating surfaces, any particulate contamination, such as dirt orsand, will lodge between the disk and the valve seat This prevents the valvefrom sealing and permits live steam to flow through the discharge port Ifpressure is not maintained above the disk, the trap will cycle frequently.This wastes steam and can cause the device to fail prematurely

The key advantage of these traps is that one trap can handle a completerange of pressures In addition, they are relatively compact for the amount

of condensate they discharge The chief disadvantage is difficulty in handlingair and other noncondensable gases

Bimetallic

A bimetallic steam trap, which is shown in Figure 22.4, operates on the sameprinciple as a residential-heating thermostat A bimetallic strip, or wafer,connected to a valve disk bends or distorts when subjected to a change intemperature When properly calibrated, the disk closes tightly against a seatwhen steam is present and opens when condensate, air, and other gases arepresent

Two key advantages of bimetallic traps are: (1) compact size relative totheir condensate load-handling capabilities, and (2) immunity to hydraulic-hammer damage

436 Steam Traps

Bimetal strip

Figure 22.4 Bimetal trap

Their biggest disadvantage is the need for constant adjustment or tion, which is usually done at the factory for the intended steam operatingpressure If the trap is used at a lower pressure, it may discharge livesteam If used at a higher pressure, condensate may back up into the steamsystem

calibra-Thermostatic or Thermal Element

Thermostatic, or thermal-element, traps are thermally actuated using anassembly constructed of high-strength, corrosion-resistant stainless steelplates that are seam-welded together Figure 22.5 shows this type of trap.Upon startup, the thermal element is positioned to open the valve and purgecondensate, air, and other gases As the system warms up, heat generatespressure in the thermal element, causing it to expand and throttle the flow

of hot condensate through the discharge valve The steam that follows thehot condensate into the trap expands the thermal element with great force,which causes the trap to close Condensate that enters the trap during sys-tem operation cools the element As the thermal element cools, it lifts thevalve off the seat and allows condensate to discharge quickly

Thermal elements can be designed to operate at any steam temperature Insteam-tracing applications, it may be desirable to allow controlled amounts

of condensate to back up in the lines in order to extract more heat from

Steam Traps 437

Figure 22.5 Thermostatic trap

the condensate In other applications, any hint of condensate in the system

is undesirable The thermostatic trap can handle either of these conditions,but the thermal element must be properly selected to accommodate thespecific temperature range of the application

Thermostatic traps are compact, and a given trap operates over a widerange of pressures and capacities However, they are not recommendedfor condensate loads over 15,000 pounds per hour

Performance

When properly selected, installed, and maintained, steam traps are relativelytrouble-free and highly efficient The critical factors that affect efficiencyinclude capacity and pressure ratings, steam quality, mechanical damage,and calibration

438 Steam Traps

Pressure Rating

As discussed previously, each type of steam trap has a range of steam sures that it can effectively handle Therefore, each application must becarefully evaluated to determine the normal and maximum pressures thatwill be generated by the steam system Traps must be selected for theworst-case scenario

pres-Steam Quality

Steam quality determines the amount of condensate to be handled by thesteam trap In addition to an increased volume of condensate, poor steamquality may increase the amount of particulate matter present in the con-densate High concentrations of solids directly affect the performance ofsteam traps If particulate matter is trapped between the purge valve and itsseat, the steam trap may not properly shut off the discharge port This willresult in live steam being continuously exhausted through the trap

Mechanical Damage

Inverted-bucket and float-type steam traps are highly susceptible to ical damage If the level arms or mechanical linkages are damaged ordistorted, the trap cannot operate properly Regular inspection and main-tenance of these types of traps are essential

mechan-Calibration

Steam traps, such as the bimetallic type, must be periodically recalibrated

to ensure proper operation All steam traps should be adjusted on a regularschedule

Installation

Installation of steam traps is relatively straightforward As long as they areproperly sized, the only installation imperative is that they are plumb If thetrap is tilted or cocked, the bucket, float, or thermal valve will not operateproperly In addition, a nonplumb installation may prevent the condensatechamber from fully discharging accumulated liquids

Condensate load greater than design •

High-pressure traps discharge into low-pressure

return

•

Internal parts of trap broken or damaged • • • •

Kettles or other units increasing condensate load •

No cooling leg ahead of thermostatic trap • •

Open by-pass or vent in return line •

Pressure regulator out of order •

Process load greater than design •

Plugged strainer, valve, or fitting ahead of trap •

Scored or out-of-round valve seat in trap •

Source: Integrated Systems Inc.

440 Steam Traps

Operating Methods

Steam traps are designed for a relatively constant volume, pressure, andcondensate load Operating practices should attempt to maintain theseparameters as much as possible Actual operating practices are determined

by the process system, rather than the trap selected for a specific system.The operator should periodically inspect them to ensure proper operation.Special attention should be given to the drain line to ensure that the trap isproperly seated when not in the bleed or vent position

Troubleshooting

A common failure mode of steam traps is failure of the sealing device (i.e.,plunger, disk, or valve) to return to a leak-tight seat when in its normaloperating mode Leakage during normal operation may lead to abnormaloperating costs or degradation of the process system A single34

steam trapthat fails to seat properly can increase operating costs by $40,000 to $50,000per year Traps that fail to seat properly or are constantly in an unloadposition should be repaired or replaced as quickly as possible Regularinspection and adjustment programs should be included in the standardoperating procedures (SOPs)

Most of the failure modes that affect steam traps can be attributed to ations in operating parameters or improper maintenance Table 22.1 liststhe more common causes of steam trap failures

vari-Operation outside the trap’s design envelope results in loss of efficiencyand may result in premature failure In many cases, changes in the conden-sate load, steam pressure or temperature, and other related parameters arethe root causes of poor performance or reliability problems Careful atten-tion should be given to the actual versus design system parameters Suchdeviations are often the root causes of problems under investigation.Poor maintenance practices or the lack of a regular inspection program may

be the primary source of steam trap problems It is important for steamtraps to be routinely inspected and repaired to assure proper operation

23 V-Belt Drives

“Only Permanent Repairs Made Here”

V-belt drives are widely used in industry and commercial applications.V-belts are utilized to transfer energy from a driver to the driven and usu-ally transfer one speed ratio to another through the use of different sheavesizes

V-belts are constructed for three basic components, which vary from maker

to maker:

1 Load carrying section to transfer power

2 Rubber compression section to expand sideways in the groove

3 Cover of cotton or synthetic fiber to resist abrasion

Understanding the construction of V-belts assists in the understanding ofbelt maintenance The standard V-belt must ride in the sheave properly Ifthe belt is worn or the sheave is worn, then you will have slippage of the beltand transfer of power, and speed will change resulting in a speed change

to a piece of equipment If a V-belt drive is located near oil, grease, orchemicals the V-belts could lose their capability through the deterioration

of the belt material, again resulting in the reduction of energy transfer andquickly resulting in belt breakage or massive belt slippage

Introduction

Belt drives are an important part of a conveyor system They are used totransmit needed power from the drive unit to a portion of the conveyorsystem This chapter will cover:

1 Various types of belts that are used to transmit power;

2 The advantages and disadvantage of using belt drives;

3 The correct installation procedure for belt drives;

442 V-Belt Drives

Driven

roll

Drivemotor

Figure 23.1 Belt drive

4 How to maintain belt drives;

5 How to calculate speeds and ratios that will enable you to makecorrections or adjustments to belt drive speeds;

6 How to determine belt length and sheave sizes when making speedadjustments

Belt Drives

Belt drives are used to transmit power between a drive unit and a drivenunit For example, if we have an electric motor and a contact roll on aconveyor, we need a way to transmit the power from the electric motor tothe roll This can be done easily and efficiently with a belt drive unit SeeFigure 23.1

Belt drives can consist of one or multiple belts, depending on the load thatthe unit must transmit

The belts need to be the matched with the sheave type, and they must betight enough to prevent slippage Examples of the different belt and sheavesizes are as follows:

1 Fractional horsepower V-belts: 2L, 3L, 4L, and 5L;

2 Conventional V-belts: A, B, A-B, C, D, and E;

Conventional cogged V-belts: AX, BX, and CX;

3 Narrow V-belts: 3V, 5V, and 8V;

Narrow cogged V-belts: 3VX and 5VX;

4 Power band belts: these use the same top width designations as the abovebelts, but the number of bands is designated by the number preceding

Figure 23.2 Examples of V-belts

the top width designation For example, a 3-ribbed 5V belt would belabeled 3/5V;

5 Positive-drive belts: XL, L, H, XH, and XXH

The size of the belt must match the sheave size If they do not match, thenthe belt will not make proper contact with the sheave and will decrease theamount of load it can transmit They may look something like the illustration

in Figure 23.2

Usually a set of numbers will follow the belt designation These numbersrepresent the actual length of the belt in inches On conventional belts, thelength is given for the inside length of the belt, and on narrow belts it isgiven for the outside length An example of this would be a 5V750 belt;the size of the belt gives it the 5V and the outside length of 75.0" gives itthe 750

More information about the specific belt dimensions can be found in the

Goodyear Power Transmission Belt Drives manual.

Belt Selection

V-Belts

V-belts are best suited for transmitting light loads between short rangesheaves They are excellent at absorbing shock When an overloadoccurs, they will act as an overload device and slip, thereby protecting

444 V-Belt Drives

Figure 23.3 Standard V-belt

Figure 23.4 Cogged belt

valuable equipment They are also much quieter than other power mission devices such as chains

trans-Because of their design, they are easier to install and maintain than otherbelt types Other than an occasional retensioning, V-belts are virtually main-tenance free When properly installed and maintained, V-belts will provideyears of trouble-free operation For an example, see Figure 23.3

Cogged Belts

Cogged belts provide even longer life than conventional V-belts Because

of their design, they run cooler than conventional belts, thereby increasingthe overall life of the belt For an example, see Figure 23.4

Joined Belts

Joined or power band belts provide a good alternative in pulsating driveswhere standard V-belts have a tendency to turn over They function like a

V-Belt Drives 445

Figure 23.5 Joined belt (VX type)

Figure 23.6 Positive drive belt

standard V-belt, with the exception that they are joined by the top fabric ofthe belt These belts can be used with the standard V-belt sheaves, makingselection and installation easy For an example, see Figure 23.5

Positive-Drive Belts

Positive-drive belts are sometimes called timing belts because they are oftenused in operations when timing a piece of equipment is critical However,they are also used in applications where heavy loads cause standard V-belts

to slip They are flexible and provide the same benefit as standard V-belts,but their alignment is more critical For an example, see Figure 23.6

Sheaves

Sheaves are wheels with a grooved rim on which the belt rides Sheavesare manufactured in various widths and diameters Some have spokes, andsome do not For an example, see Figure 23.7

Sheaves are made of cast steel for heavy-duty applications For lighter cations, they are forged out of steel plate Cast-iron sheaves are always used

appli-in applications where fluctuatappli-ing loads are present They provide a flywheeleffect that minimizes the effects of fluctuating loads

446 V-Belt Drives

Figure 23.7 Positive drive belt

When they are mounted to a shaft, sheaves should be straight and have little

or no wobble For drives where the belt enters the sheave at an angle, groove sheaves are available These are especially useful when the belts mustturn or twist

deep-Deep-groove sheaves can be used anywhere belt stability is a problem Insome cases, one drive shaft drives more than one driven shaft When thisoccurs, more than one sheave can be mounted on one shaft This is nec-essary only when sheaves of more than one size are needed If the drivesheaves are the same size, one multibelt sheave can be used

Most sheaves are balanced and capable of belt speeds of 6,000 feet perminute or less If you note excessive vibration during operation or excessivebearing wear, you may need to balance or replace the sheaves

Power Train Formulas

Shaft Speed

The size of the sheaves in a belt drive system determines the speed ship between the drive and driven sheaves For example, if the drive sheavehas the same size sheave as the driven, then the speed will be equal SeeFigure 23.8

relation-If we change the size of the driven sheave, then the speed of the shaft willalso change We know what the speed is of the electric motor and the size