MPA Logo, San Francisco Maritime National Park Association, USS Pampanito, Historic Ships at Hyde Street Pier, Education Programs Maritime Park Association Home Page Maritime Park Association Home Page Events Maritime Park Association Home Page Maritime Park Association Home Page Maritime Park Association Home Page Volunteer Membership Donate Maritime Park Association Home Page USS Pampanito Submarine Historic Ships at Hyde Street Pier Education Programs About Maritime Park Association Home Page Directions to Maritime Jobs at Maritime Facility Rental at Maritime Trustees of the Association Calendar Press Room Store Maritime Map
14
DETAILS OF AIR-CONDITIONING SYSTEM
 
A. DESCRIPTION OF PLANT
 
14A1. The air-conditioning cycle. The Freon 12 refrigerant cycle in the air-conditioning system is the same as that in the refrigeration system. In general, the mechanical circuit of equipment is also similar; the main difference is that the air is brought by forced ventilation through ducts to the evaporators and returned through ducts to the rooms.

14A2. The air-conditioning plant. The air conditioning plant consists of the following main elements:

1. Two compressors, York-Navy Freon 12, enclosed single-acting vertical, two cylinders 4-inch bore x 4-inch stroke, rated at 4 refrigeration tons each.

2. Two condensers, York-Navy Freon 12, horizontal shell-and-tube 4-pass type.

3. Two receivers, York-Navy Freon 12 type.

4. Four evaporators, with finned cooling coils in two casings.

5. Two conning tower evaporators, in one casing.

14A3. Double system arrangement. The main elements are connected as two separate systems, each containing all necessary valves, gages, and controls for automatic operation. The cooling coils of these two systems, how ever, are placed side by side in an evaporator casing and, though appearing to be a single unit of coils, are nevertheless entirely separate. Thus either of the two systems may be operated alone, with its cooling action taking place in the evaporator casing. There are two such casings, located in different rooms in the submarine. Figure 14-1 (inserted at the back of the book) shows the complete system, with all piping connections and the location of all elements, valves, and devices. This diagram illustrates clearly the double arrangement. A separate diagram shows the ducts

  and air distribution system, which are described later.

14A4. Interconnection of double system. The two systems, while ordinarily set to operate individually, are interconnected. On the 200 class submarines, the interconnecting pipes run between 1) the discharge lines of the compressors; 2) the outlet lines of the condensers; 3) the inlet or suction lines to the compressors. Shutoff valves in these interconnecting, pipes permit any of the main elements to be cut out of one system and put into the other, in case of necessity.

Figure 14-1 shows these interconnecting pipes and valves clearly; they are left uncolored in the diagram for the sake of clarity. The colored piping indicates the circuits in which an actual flow of refrigerant is taking place during normal operation. There is no flow in the interconnecting pipes unless their shutoff valves are opened; normally they are closed. On the 300 class submarines, the inter connecting pipes run between 1) the discharge lines of the compressors, and 2) the outlet lines of the condensers. There is no interconnection between the suction lines of the compressors.

14A5. The capacity of the air-conditioning system. The capacity of the system is 8.0 refrigeration tons with the two compressors operating at 330 rpm; and 6.4 refrigeration tons with the two compressors operating at 265 rpm; 10 gallons per minute of 85 degrees F water per refrigeration ton are circulated through condensers; and suction pressure corresponds to an evaporation temperature of 35 degrees F. Since most of the mechanical parts are the same as those in the refrigerating system, only the different parts are described.

 
B. THE COMPRESSORS
 
14B1. General description. Each of the two compressors is quite similar to the refrigeration system   compressor. No separate illustration of them is given, since the main difference
 
100

lies only in the size, which is as follows:

1. Bore, 4 inches; stroke, 4 inches.

2. Drive, by 5 V-belts from a two-speed 4.9- to 4.1-hp electric motor, 250 (175-345) volts direct current (d.c.).

3. Lubricating oil charge, 10 pints of Navy Contract Oil, Symbol No. 2135, or equivalent.

14B2. Suction and discharge valves. Attention is called to the fact that in the 4 x 4 air conditioning compressor, the valve diaphragms or disks are exactly alike in both valves, and hence are interchangeable when new. Each valve has three disks, slightly

  dished and assembled in the following order; bottom disk, concave downward, small spacer; middle disk, concave upward; top disk, concave downward. The disks are 3 3/4 inches in diameter and contain three concentric circles of 5/32-inch holes, that must be aligned in assembly.

It is not good practice to permit a Freon 12 compressor to remain idle for an extended period of time. Compressors should be operated at least once a week. Therefore, if duplicate or standby compressors are furnished, they should be operated alternately, changing from one to the other at least every week.

 
C. THERMOSTATIC EXPANSION VALVE
 
14C1. The thermostatic expansion valve. Two types of this valve are in use, one for refrigerating, called the internal equalizer; and the other for air-conditioning, called the external equalizer. A general description is given first, then a detailed description of each type.

The remote bulb assembly (sometimes called the power assembly) contains Freon 12, and is attached to the suction line at the exit of the evaporator coil. Since Freon 12 has an exact temperature-pressure relationship, any variation in temperature of the suction line at the point of attachment produces a corresponding variation of pressure within the bulb. This pressure is communicated to the upper side of the diaphragm in the expansion valve. The lower side of the diaphragm (with airtight separation from the upper) is part of the regular refrigeration fluid circuit. Therefore any pressure difference between both sides causes the diaphragm to move. This, in turn, moves the valve stem, permitting more or less liquid Freon 12 to flow through.

The thermostatic expansion valve controls the quantity of liquid refrigerant that is admitted to the evaporator according to changes in the superheat of the suction vapor leaving the evaporator.

This valve is designed to maintain a constant degree of superheat in the refrigerant vapor leaving the cooling coils, regardless of suction pressure. Thus its function is two fold:

  1. Automatic expansion control.

2. Prevention of liquid refrigerant from surging through the evaporator to the compressor. It acts also to disperse the liquid Freon 12 in small droplets for easier and quicker evaporation and divides the high- and low-pressure sides of the system at this point.

The piping connections include a liquid strainer and a solenoid valve, with shutoff valves for servicing the strainer, solenoid valve, or thermostatic expansion valves; also manually operated valves and bypass for use in case it is desired to examine the thermostatic expansion valves, solenoid valve, or to clean the strainer.

14C2. Internal equalizer. This type of expansion valve is illustrated in Figure 7-10. After the liquid Freon 12 enters the valve and passes through the orifice, it is at low-pressure level of the evaporator. A port, or channel, bored through the valve seat retainer makes the spring chamber a part of the low-pressure line. The low-pressure refrigerant entering the spring chamber adds its pressure to the pressure of the spring on the diaphragm. Opposing this combined internal pressure is the pressure from the remote bulb on the other side of the diaphragm.

14C3. External equalizer. An expansion valve is installed at the entrance of the evaporator tubing, and its bulb is attached at the exit of the evaporator tubing. Theoretically, the pressure inside the evaporator should be

 
101

constant. Any loss of pressure between the two ends of the evaporator coil would be of great importance as far as the proper working of the expansion valve is concerned.

In a refrigeration system, the evaporator tubing is usually of fair-sized diameter. Any pressure drop therein would be negligible. But in an air-conditioning system, the evaporator tubing is likely to be of smaller diameter, with restricted return bends. More over, the tubing is arranged in several separate banks joined by distributor headers from the single entrance pipe coming from the receiver. Such conditions cause a sizable pressure drop between the two ends of the evaporator, which, if not corrected, produce a material increase in the superheat of the vapor.

The external equalizer is designed to offset this undesired condition. Figure 14-2 illustrates the external equalizer type of expansion valve. In this type, the port in the seat retainer is eliminated. Instead, there is an opening through the wall of the valve directly into the spring chamber. Fastened to this opening is a small diameter tubing, the other end of which communicates with the evaporator

  coil just beyond the point of greatest pressure drop. This point is usually just beyond the distributor header at the entrance end of the evaporator, because most of the drop occurs across this small region. With this supplementary connection, the pressure on the underside of the valve diaphragm approximates the mean evaporator pressure. The pressure drop across the distributor header still exists, of course, but its effect on the valve diaphragm has been balanced out, so that the superheat is back to normal, and the capacity of the system is not decreased.

14C4. Adjusting the thermostatic expansion valve. Navy specifications call for 10 degrees of superheat and this setting is usually made at the factory. If it becomes necessary to adjust the superheat setting, remove the seal nut and manipulate the adjusting stem. Turning this stem clockwise (tightening the spring) increases the superheat and reduces the flow through the valve. Conversely, turning the stem counterclockwise reduces the superheat and increases the flow of liquid through the valve. Once set, it is seldom necessary to readjust.

Figure 14-2. Thermostatic expansion valve, external equalizer.
Figure 14-2. Thermostatic expansion valve, external equalizer.
 
102

14C5. Thermostatic expansion valve trouble. The thermostatic expansion valve should function without any difficulty if the system is free of dirt or foreign matter and contains no moisture. Presence of dirt or foreign matter between the seat and the valve prevents it from closing tight. Likewise, the presence of moisture in the system causes a freeze-up at the valve port and blocks the passage of Freon 12.

The system does not operate satisfactorily unless there is at least a 60-psi differential in pressure, between the high-pressure and low-pressure sides of the valve.

If it is evident that no Freon 12 is passing

  through the expansion valve, the valve should be disassembled, after closing the proper cut out valves, by removing the capscrews connecting the power assembly to the body. This permits the valve cage assembly to be examined for the presence of frost, ice, or dirt.

Due caution should be taken in reassembling the thermostatic expansion valve to see that all gaskets are properly placed, and that the valve cage assembly is properly aligned. Gaskets must be of the prescribed material.

It should be noted that these valves are delicate instruments and do not withstand rough usage. They should be handled with care.

 
D. SUCTION PRESSURE REGULATING VALVE
 
14D1. Purpose. The suction pressure regulating valve (see Figure 14-3), used only in the air-conditioning system, is a constant pressure device. Four of these were formerly used in the complete system, there being one   installed in the suction line from each bank of the air-conditioning evaporators. On the 300 class submarines, only one of these valves is now used, and it is located in the pump room, on the suction line of the No. 1
Figure 14-3. Suction pressure regulating valve.
Figure 14-3. Suction pressure regulating valve.
 
103

air-conditioning unit. Normally this valve is by passed and is cut into the system only during the time that the No. 1 air-conditioning unit is cross-connected to the refrigerating system.

By having a suction pressure regulating valve installed in the suction line of the No. 1 air-conditioning unit, it is possible to operate the refrigerating system, with a suction pressure of about 5 pounds, and at the same time, to operate the No. 1 air-conditioning system, with a suction pressure of 35 pounds.

The suction pressure regulating valve serves the purpose of maintaining a substantially constant vaporizing temperature in the evaporator coil to which it is connected, regardless of the temperature prevailing in the suction line itself, or of sudden load changes or suction pressure fluctuations.

14D2. Operation. The type of constant pressure valve used is known as a pilot-operated piston valve. Figure 14-3 shows the disposition of the various parts. The pilot circuit is a separate channel in the body of the valve leading up from the inlet side, across the top where a filter is placed, and into the space under the diaphragm. The operation of the valve is as follows:

The main valve is normally held in a closed position by the main valve spring and the evaporator pressure under the main valve seat. The evaporator pressure is also transmitted through the pilot channel to the diaphragm. When the pilot valve is closed by pressure of the diaphragm, this evaporator pressure cannot flow down through the opening in the center of the pilot seat into the main valve. The closing pressure on the diaphragm is regulated to the desired value by the adjusting stem.

When the evaporator pressure exceeds the value of this pilot diaphragm adjustment, the diaphragm lifts, permitting the evaporator pressure to act down through the pilot seat, and the port into the main valve chamber to the top of the piston. Since the piston is of larger area than the main valve opening, it overcomes the combined closing forces of the spring and evaporator pressure under the seat, thus opening the valve. The reverse action takes place

  when the evaporator pressure falls below the setting of the pilot adjustment.

However, in actual operation, this action does not take place in complete steps of opening and closing. Normally, the piston assumes an intermediate floating position, responding to fluctuations in the evaporator pressure; these fluctuations are balanced out and the resulting pressure is maintained at a substantially constant value asset by the adjusting stem. Since Freon 12 has a strict pressure-temperature relationship, this automatic action maintains the temperature within the evaporator coil at a nearly constant level.

14D3. Internal and external pilot circuits. The suction pressure regulating valve may be used with either an internal or external pilot circuit. As an internal pilot circuit, it is used as described, with the evaporator pressure coming through the internal channel in the valve body, and the plug inserted.

With the external pilot circuit, a 3/8-inch o.d. tubing is screwed into the connection of the channel at the top of the valve (shown closed by a screw plug in Figure 14-3). The other end of the 3/8-inch tube is connected to the suction line. This external pilot circuit is used when the installation must be at some distance from the evaporator, or where a considerable drop in pressure may be expected. The connection in the suction line should be at a point where low refrigerant velocity exists.

When used with the external pilot circuit, the internal circuit must be closed. This is done by rotating the cage and the body gaskets. The cage flange and body gaskets contain holes that may be aligned with the channel. They must be so aligned when the valve is used with the internal pilot circuit. When the external pilot circuit is used, the cage and body gaskets must be rotated so that the holes are out of alignment, thus shutting off the internal channel.

In submarine installations, the internal pilot circuit ordinarily is used. However, if the external pilot circuit would give much better

 
104

operation of the system, the external tubing is easily attached.

14D4. Adjustment. The suction pressure regulating valve is designed to operate properly at light loads. A minimum differential of 2 pounds between evaporator and suction pressures is sufficient for proper operation.

The pressure adjustment range runs from 2 psi to 70 psi. Rotating the adjusting stem clockwise gives a higher pressure setting, and vice versa. One complete turn of the adjusting stem changes the setting by approximately 4 pounds.

When adjusting, insert a pressure gage in the external pilot tube connection, first removing the plug or tubing. Be sure to allow ample time for the system to stabilize itself between adjustments. If the valve fails to respond to an adjustment, check the suction pressure to make sure that the compressor is actually capable of producing a pressure lower than that desired in the evaporator, remembering that a 2-pound differential is sufficient.

  Be sure to replace the seal cap after adjustment.

14D5. Cleaning. All service operations may be performed on this valve without removing it from the line. The pilot channel filter may be removed for cleaning, using a screwdriver. The entire pilot valve housing may be removed by using an ordinary wrench on the hexagon at the top. The diaphragm and pilot seat may be cleaned, if necessary, with a soft, clean cloth.

The main upper body is removed by taking out the four capscrews. Note that the piston has a loose fit and slides freely in the housing; be careful that it does not drop. The cage and inlet strainer may now be lifted out for cleaning.

In reassembling, be sure to replace all gaskets. Be sure that the holes in the cage flange and body gaskets are properly placed, in line with the channel for the internal pilot circuit, and out of line for the external pilot circuit.

 
E. THE EVAPORATOR
 
14E1. Construction. The air-conditioning evaporator is constructed to provide a large cooling and condensing surface in a small space. The overall dimensions are, roughly forward coils, 5 feet 7 inches long, 11 inches high, 9 inches wide. The after coils are of shorter length, about 3 feet 6 inches, but of the same height and width as the forward coils. These coils are part of the Freon 12 piping within this space. Around the coils is the evaporator casing into which the inlet and outlet air ducts are connected.

The coil piping passes through plates or fins of very thin metal, stacked six to the inch the whole length of the coils. These fins are held in place by small dimples and tin-tipped solder. The coils are wedged tightly to the fin plates in assembly. The air flow through the evaporator is parallel to the fins, but the fins are bent slightly zigzag (see Figure 14-4) to create a turbulent air flow, thus causing all the air to come in contact with the cooling surfaces. The heat, from the air passes by conduction through all of these fins to the cooling coils proper or banked refrigerant

  main, and through it to the refrigerant within.

The cooling coils, while spaced evenly, actually form two completely separate sets, going to each of the two compressors. The inlet from each of the two receivers divides at the distributor cup into four branches which run in parallel within the evaporator, joining back to a single pipe at the outlet. Figure 14-4 shows this double set construction clearly, and the lower view shows the coiled path taken by a single one of these branches.

a. Distributor cup. The distributor cup (not shown in Figure 14-4) is a small compartment, the entrance from the single inlet pipe being a small orifice or hole about one third the diameter of the inlet pipe. The four outlets to the branches from the distributor cup are about the same size as the orifice. This arrangement tends to provide an equal pressure distribution in the four branches.

14E2. New type evaporator. A newly developed design of evaporator is shown in Figure 14-5. In this type, the fins are separate small disks around the piping, instead of single

 
105

plates across the whole evaporator. This construction permits quicker and better cleaning. There is also a new type of distributor cup, an inner cup, that overflows and fills the outer cup, and goes out into the branches, the ends of which project down into the cup.   These ends have small holes at the top of the cup and are open at the lower extremity (see enlarged view in Figure 14-5).

The reason for this new design of cup is that while theoretically there should be no throttling action or expansion of liquid into

Figure 14-4. Air-conditioning evaporator.
Figure 14-4. Air-conditioning evaporator.
 
106

flashgas while flowing into a cup, practically, there usually is some. The holes into the branch ends at the top of the cup permit any such flashgas to be distributed equally into the four branches. This design also has a low-pressure drop across the distributor header. In installation, these cups should be set upright and not turned on their sides, which would cause gas binding, and some of the branches would lack their proper share of liquid.   14E3. Conning tower evaporators. Two evaporators, contained in a single casing, are located in the conning tower. They are connected to the liquid and suction lines of No. 1 and No. 2 air-conditioning plants, respectively. Each evaporator has its own expansion valve and solenoid valve; however, there is no thermostat. The solenoid valve is controlled by a hand-operated switch and can be operated manually only.

The installation and design of conning

Figure 14-5. Air-conditioning evaporator, new type.
Figure 14-5. Air-conditioning evaporator, new type.
 
107

tower air-conditioning units vary with each class of vessel. Therefore, no detailed   description can be given to cover each installation.
 
F. CLEANING THE EVAPORATOR
 
14F1. Maintenance and cleaning of cooling coils. An accumulation of dust or organic material on the surfaces of a cooling coil decreases the quantity of heat that can be transferred, and lowers the operating efficiency of the coil. Even a thin film on the surface reduces the capacity to an undesirable extent. This is particularly applicable to cooling coils since the condensation of atmospheric moisture on the coils tends to accelerate the accumulation of foreign matter. The presence of this foreign matter also tends to restrict the air flow.

The cooling coils installed on submarines should be cleaned in accordance with the following instructions.

14F2. Frequency of cleaning. Coils should be inspected monthly and cleaned as often as necessary, as indicated by the periodic inspection. In any case, the coils should be cleaned every three months.

14F3. Access for cleaning. Cooling coils should be provided with ready access to facilitate inspection and cleaning. If possible, a section of ducts on either side of the coils should be portable. If this is not possible, the bottom of the ducts on both sides of the coil should be readily removable. In cases where such access does not already exist, it should be provided by the ship's' force or listed as a work item for the next overhaul.

14F4. Cleaning procedure. Shut off the air supply through the coil and remove the portable section of duct or portable plate on each side. The recommended cleaning agents are nontoxic and may be safely used in closed compartments with ventilation operating, whenever conditions do not permit open

  doors and hatches in the compartment.

When cleaning the cooling coils, do not shut off the compressors as cleaning agent RM 70 is volatile.

Prepare a bucket of RM 70 solution, a nontoxic solvent, in warm water (about 110 degrees F) in the ratio of 4 ounces of RM 70 to 1 gallon of water.

Provide a spray lance or paint gun with a piece of hose sufficiently long to reach conveniently into a bucket. Attach the inlet air connection to a source of air at about 60 pounds. Bleed the air so that a fine spray is produced. Wet down the entire coil surface, working from the air discharge side of the coil, and allow to stand for about five minutes. Readjust the gun to produce a spray of high velocity, and wash the coils with clean water, blowing from the air discharge to the air inlet side. If found necessary, provide some means to prevent the blast of dirty solution from carrying past the coil and up the supply duct. Drain off and wipe away any of the solution remaining. Allow the coils to dry and replace the access plates. The Bureau of Aeronautics is now developing an equivalent of RM 70 which does not require the use of critical materials.

If RM 70 is not procurable, the coil may be cleaned in a similar manner using a solution of trisodium phosphate, in the ratio of 1/2 pound of crystals to 3 gallons of warm water (about 100 degrees F). If the trisodium phosphate solution is used, the operation requires more time and is more difficult. In addition, the coils should be thoroughly rinsed with warm water, using the gun, after cleaning with the solution.

 
108

Previous chapter
Previous Chapter
Sub Refrig. Home Page
Sub Refrig. Home Page
Next chapter
Next chapter


Copyright © 2013, Maritime Park Association
All Rights Reserved
Legal Notices and Privacy Policy
Version 1.10, 22 Oct 04