The procedure for cleaning saltwater heatersis as follows:1. Remove the waterheads.2. Insert the special cleaning tool in the tubeand drive it with a 250 to 300 rpm motor. Themotor should be of the reversible type.3. Feed a light stream of water into theopposite end of the tube to wash the scale fromthe cutting tool and out of the tube. A light streamof compressed air may be substituted in place ofthe water. Care should be taken not to drive thetool too fast and to be certain that the tool isstraight when it is inserted into the tube.An 8 to 10 psig hydrostatic test should be per-formed on the shell of the saltwater heater beforereplacing the heads. If a greater test pressure isused, the relief valve will have to be plugged orremoved.Cleaning Feed BoxesIf feed flow is below normal and the distillerfeed pump discharge is normal, the first-stageflash orifices may be plugged. Fouling of thesecond-stage orifices may be evidenced by waterbacking up into the first stage; however, thesecond-stage orifices are larger and will not be asreadily plugged. Water backing into the first stagemay also be caused by insufficient pressure dif-ference between the stages.Since the temperatures that exist in the feedboxes are well below the range in which saltwaterscale forms, the only plugging or fouling expectedat the orifices would come from the introductionof foreign matter into the system. Should theorifices in either stage become plugged, it will benecessary to remove the access plate at the frontof the unit, remove the perforated plates from thefeed box, and remove the obstructing materialfrom the orifices. The feed boxes are constructedso that the front can be readily removed foraccess to the orifices.AUTOMATIC PRESSURECONTROL DEVICESMost shipboard systems and machinery areprotected by pressure or temperature controldevices. Their maintenance and operation are theresponsibility of the EN1 or ENC on duty. Of thevarious types of pressure and temperature con-trol devices, the temperature control regulator,the relief valve, and the reducing valve are thetypes that you will encounter more often. Sincetemperature regulators were discussed in an earlierchapter, we will not cover them in this chapter.We will discuss only the relief valve and the reduc-ing valve. Remember, the information given inthis chapter is general. More detailed informationcan be obtained from the manufacturer’s technicalmanual.All reducing valves should be inspected,cleaned, and repaired semiannually, or wheneverthey do not operate properly.RELIEF VALVESRelief valves are designed to open automatic-ally when the pressure in the line or the unitbecomes too high. They are commonly installedin steam, water, and oil lines, and on various unitsof machinery where pressure must not exceed acertain limit. Relief valves prevent the building-up of an excessive pressure which may be causedby such conditions as the sudden closing of anoutlet valve or the failure of a reducing valve.There are many different types of relief valves,but most of them consist of a valve body contain-ing a disk or ball. Under normal pressure condi-tions, the compression of a coil spring holds thedisk or ball on its seat. When the pressure in avalve exceeds the resistance of the spring, the diskor ball lifts off its seat and the pressure is reduceduntil it falls below the pressure for which the valveis set.Relief valves should be set at the liftingpressure specified by the manufacturer. The ten-sion on the valve spring can be adjusted by meansof an adjusting nut. The nut should be lockedwhen the desired setting is attained. Since the set-ting for a specific valve will depend on the designof the valve and its use, the instructions in theapplicable manufacturer’s technical manualshould be followed when any relief valve is beingset.Continual lifting (popping) of a relief valveindicates either excessive pressure or malfunc-tioning of the valve. Either condition should becorrected immediately. A relief valve which is notChapter 7—AUXILIARY MACHINERY7-33
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