RD4ED502

Capacity regulators (hot gas bypass)Type PMC and CVC

REFRIGERATION AND AIR CONDITIONING Technical leafl et

2 RD4ED502 Danfoss A/S (RC-CMS / MWA), 11-2004

Technical leaflet Capacity regulators (hot gas bypass), type PMC and CVC

Contents Page

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Technical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Ordering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Hot gas capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Design/Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Dimensions and weights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Danfoss A/S (RC-CMS / MWA), 11-2004 RD4ED502 3


Introduction

The function of the capacity regulator is to match the fixed output of the compressor and the varying load on the system. This function is obtained when the PMC and CVC is installed in a bypass line between the discharge and suction sides of the compressor.If the load on the evaporator, and with it the load on the compressor, falls, an "artificial" load in the form of hot gas from the high pressure side of the compressor is applied to the evaporator or compressor.

The PMC and CVC is used for capacity regulation in refrigeration, freezing and air conditioning plant for ammonia and fluorinated refrigerants.The PMC is a servo-operated regulator with screwed-on pilot valves.

PMC and CVC can be used in all types of refrigeration plant:

With direct expansion

With pump recirculation

With natural circulation

Features Accurate regulation

High capacity and operating range

Independent of condensing pressure variations

High flexibility

Screw in pilot

Simple adjustment and build-up

Technical data

1) In addition to the refrigerants specified, other fluorinated refrigerants can be used within the pressure or temperature range of the valves.

2) Max. working and test pressures refers to the high pressure side connection (PS: 28 and p': 42 bar) and reference pressure (PS: 17 and p': 26.5 bar) which must be connected to the low pressure side of the system.

Materials Gaskets are non-asbestos

Pressure Equipment Directive (PED)The PMC and CVC valves are approved in accordance with the European standard specified in the Pressure Equipment Directive and are CE marked. For further details / restrictions - see Installation Instruction.

Valve body EN-GJS-400-18-LT or cast iron GG 25

PMC and CVC valves

Nominal bore DN ≤ 25 (1 in.)

Classified for Fluid group I

Category Article 3, paragraph 3

Type Refrigerants 1)

Opening diff.pressure

∆p bar

P-band

Temperatureof medium

°C

Max. workingpressure

PS 2)bar

Max.test pressure

p'

bar

PMC 1 and PMC 3R22

R134aR404A

R717 (NH3)R12

R502ect.

Withbuilt-on CVC:

Approx. 0.2 bar–50 → +120 28 42.0

CVC –50 → +120 17/28 26.5/42.0

EVMa.c.: 10Wd.c.: 20W

a.c.: 0 → 21d.c.: 0 → 14

–50 → +120 35 46.0



Ordering PMC main valves

1) The kv value is the water flow in m3/h at a pressure drop across the valve of 1 bar (ρ = 1000 kg/m3).

The code nos. stated apply to main valve type PMC incl. flange gaskets and bolts.

The rated capacity is given for an evaporating temperature of te = −10°C, a condensing temperature of tc = +32°C and an offset (= suction temperature reduction ∆ts) of 4 K.

Pilot valves

1) The code no. stated apply to pilot valve type CVC incl. pilot signal connector.2) When ordering, please state code no., voltage and frequency.

Flange sets

1) Code no. applies to a flange set consisting of one inlet flange and one outlet flange.

ExamplePMC 3 size 12, code no. 027F0152+ 1 in. flange set, code no. 027N1225+ CVC, code no. 027B1070+ EVM, code no. 027B1122, 220 V, 50 Hz+ ∅ 6.5 / 10 mm pressure gauge connection,code no. 027B2035.

PMC 1 PMC 3

Size GG-25 EN-GJS-400-18-LT GG-25 EN-GJS-400-18-LT

PMC 5 027F0140 027F3045 027F0150 027F3049

PMC 8 027F0141 027F3046 027F0151 027F3050

PMC 12 027F0142 027F3047 027F0152 027F3051

PMC 20 027F0143 027F3048 027F0153 027F3052

Valve sizeRated replacement capacity in kW kv value

R22 R134a R404A R12 R502 R717 m3/h1

PMC 5 36 19 36 20 34 96 1.7

PMC 8 67 35 65 37 61 179 3.2

PMC 12 82 47 88 51 83 244 4.2

PMC 20 140 74 136 78 130 367 6.5

Description Range Code no.

Pilot valve type CVC with ∅ 6.5/10 mm weld signal connection

−0.45 → +7 bar 027B1070 1)

Pilot valve type EVMa.c. 027B1122 2)

d.c. 027B1124 2)

Valve type Flange typeWeld flange set Solder flange set

in. Code no. 1) in. Code no. 1) mm Code no. 1)

PMC 1 and 3 12

3/4 027N1220 7/8 027L1223 22 027L1222

1 027N122511/8 027L1229 28 027L1228

11/4 027N1230

AccessoriesDescription Code no.

Pressure gauge connector Ø 6.5 / Ø 10 mm weld / solder

027B2035

Pressure gauge connector ¼ in. flare (self-closing) Must not be used for ammonia

027B2041

Pressure gauge connector, cutting ring connection6 mm

10 mm027B2063027B2064

Pressure gauge connector ¼ NPT 027B2062

External pilot connection 027F1048



Sizing

The stated PMC hot gas capacities assume that the hot gas is injected ahead of the evaporator.The thermostatic expansion valve compensates for the heat the hot gas transfers to the evaporator by increasing liquid injection. In this way the superheat at the evaporator outlet is kept more or less constant.Capacities are thus made up of the PMC regulator capacity + expansion valve compensation.Capacities are given for an offset (= suction temperature reduction ∆ts) of 4 K.

Qh = mb(h2-h4) (kW) whereQh = hot gas capacity or replacement capacity given in table in kWmb = flow through PMC in kg/sh2-h4 = enthalpy difference in kJ/kg

Suction pressures in the table relates to suction pressure / suction temperature after the reduction.If a smaller offset than 4 K is required, multiply the capacity found at ∆ts = 4 K by a correction factor k.If the correction factors are not changed as a function of the suction temperature reduction ∆ts, the proportional band of the regulator is fully utilized.The proportional band of the regulator is approx. 0.2 bar.

Selection exampleAn R134a unit for compressed air drying must be capacity regulated from 100% to 0% using hot gas injection direct into the evaporator after the expansion valve. The compressor has no internal capacity regulation.Compressor capacity, Qc = 12 kW at te = 0°C and tc = +30°C.Min. suction temperature, ts min. = 0°C.Max. off-set, ∆ts max. = 2 K.Min. evaporator load, Qe min. = 0 kW.Necessary PMC replacement capacity, Qh = 12 − 0 = 12 kW.From the capacity table, it can be seen that PMC size 5 produces 19 kW at ts = 0°C, tc = +30°C and ∆ts = 4 K.Correction factor k for off-set ∆ts = 2 K is given as 0.7.The final replacement capacity Qh for PMC size 5 thus become 19 × 0.7 = 13.3.A PMC size 5 will therefore produce the same as the compressor, i.e. 12 kW at an off-set a little lower than 2 K.

.

.



Hot gas capacity

Hot gas / replacement capacity for suction temperature reduction, off-set ∆ts = 4 K.

Type PMC 1 and PMC 3

R22

Correction factor k for different off-set (suction temperature reductions)


R134a

SizeSuction temp. ts after

temperature reduction°C

kg/s kW

Condensing temperature tc °C

20 30 40 50 20 30 40 50

5

+100

-10-20-30-40

0.1110.140.140.1380.1370.137

0.1840.1820.1810.1810.170.18

0.2320.2310.2310.2310.2290.229

0.290.2890.2890.2890.2890.289

232929292929

363636363636

454545454545

555555545454

8

+100

-10-20-30-40

0.1920.2570.2570.2530.2530.251

0.3370.3330.3330.3330.330.33

0.4250.4240.4240.4240.4240.397

0.5340.5320.5320.5320.5320.397

385454545454

676767676767

838382828277

101101101101101

76

12

+100

-10-20-30-40

0.2390.3480.3480.3430.3390.339

0.4550.450.450.450.4470.364

0.5740.5730.5730.5730.5380.393

0.7220.720.720.720.5410.4

497272727373

898989899073

111111111111104

77

139139139139102

75

20

+100

-10-20-30-40

0.3350.530.5370.530.4640.369

0.6880.6940.6940.6940.530.399

0.8850.8850.8850.7330.5680.41

1.1121.1120.9220.7150.5670.414

67108108108

9979

130140140140107

80

173173173140108

78

216216173140108

79

Refrige-rant

Suction temp. ts after temperature reduction

°C

tc = 20°C and 30°C tc = 40°C and 50°CSuction temperature reduction ∆ts k

1 2 3 4 1 2 3 4

R22

+100

-10-20-30-40

0.40.50.50.40.40.3

0.70.90.90.70.70.6

0.91.01.00.90.90.8

1.01.01.01.01.01.0

0.60.50.50.50.40.4

0.90.70.70.70.60.7

1.00.90.90.90.80.8

1.01.01.01.01.01.0

5

+100

-10-20-30

0.0190.0720.0920.0920.092

0.1220.120.1180.1180.118

0.1560.1540.1520.1510.151

0.1940.1920.1920.1920.192

315151515

1919191919

2424242424

2929292929

8

+100

-10-20-30

0.0350.1610.1690.1690.169

0.2240.220.2180.2180.218

0.2850.2810.280.280.278

0.3580.3540.3530.3530.353

526282828

3435353535

4344444444

5254545454

12

+100

-10-20-30

0.0470.2030.2280.2280.228

0.3020.2990.2940.2940.294

0.3850.380.3780.3780.332

0.4840.4780.4780.4780.359

733373737

4647474747

5858606052

7273737354

20

+100

-10-20-30

0.0760.2640.3320.3320.278

0.4210.460.4550.4030.32

0.5940.5870.5840.4660.358

0.7470.7390.6360.5050.374

1242555545

6573746652

8990917356

113113

967757



kg/s kWCondensing temperature tc °C

20 30 40 50 20 30 40 50


Refrige-rant


°C

tc = 20°C and 30°C tc = 40°C and 50°C

Suction temperature reduction ∆ts k1 2 3 4 1 2 3 4

R 134a

+100

-10-20-30

0.10.30.30.30.2

0.40.70.60.60.6

0.80.90.80.80.8

1.01.01.01.01.0

0.40.40.30.30.2

0.80.70.60.60.5

1.00.90.80.80.8

1.01.01.01.01.0



Hot gas capacity(continued)

Hot gas / replacement capacity for suction temperature reduction, off-set ∆ts = 4 K.




20 30 40 50 20 30 40 50


R404A

5

+100

−10−20−30−40

0.1510.1840.1820.1790.1780.178

0.2350.2340.2330.2310.230.23

0.2950.2940.2920.2910.2910.291

0.3730.370.3680.3670.3670.367

232828282828

343636363636

434344434343

505151515151

8

+100

−10−20−30−40

0.2660.3370.3330.3280.3280.328

0.430.4270.4250.4250.4250.425

0.5430.5390.5360.5350.5350.535

0.6850.680.6760.6760.6760.59

395152525252

636565656565

787979797979

939394949482

12

+100

−10−20−30−40

0.3330.4540.4490.4430.4430.443

0.5770.5790.5750.5750.5740.53

0.7340.730.7250.7250.7250.544

0.9270.9210.9150.9150.7440.569

496971727272

858688888879

106107107107107105

122122122122104

79

20

+100

−10−20−30−40

0.4350.6880.6940.6850.6590.511

0.8710.8920.8860.8860.7130.557

1.1321.1251.1180.9280.730.556

1.4291.4181.1910.9410.8750.569

65104109110107

82

125136136136113

84

159170170136105

82

193193170136125

79


Refrige-rant


°C

tc = 20°C and 30°C tc = 40°C and 50°CSuction temperature reduction ∆ts K

1 2 3 4 1 2 3 4

R404A

+100

−10−20−30−40

0.40.50.50.40.40.3

0.70.90.90.70.70.6

0.91.01.00.90.90.8

1.01.01.01.01.01.0

0.60.50.50.50.40.4

0.90.70.70.70.60.7

1.00.90.90.90.80.8

1.01.01.01.01.01.0

5

+100

−10−20−30−40

0.050.0570.0550.0540.0540.054

0.0770.0730.0720.0710.0710.071

0.0980.0970.0940.0940.0940.094

0.1250.1230.1210.1210.1210.121

637373737373

969696969696

124124124124124124

158158158158158158

8

+100

−10−20−30−40

0.0870.1020.1010.10.10.1

0.140.1360.1330.1320.1320.115

0.180.1780.1730.1730.1730.129

0.230.2270.2240.2240.1950.137

111141141141141141

179179179179179154

230230230230230166

282282282282243179

12

+100

−10−20−30−40

0.1090.1390.1370.1350.1350.11

0.1890.1830.1810.1790.1770.122

0.2450.2410.2340.2340.190.13

0.3120.3060.3030.2660.1960.139

139186186186186151

244244244244244162

313313313313255174

383383383336244174

20

+100

−10−20−30−40

0.1440.2130.2110.2070.1720.12

0.2870.2830.2790.2440.1890.121

0.3770.3720.3620.270.1970.126

0.480.4730.3590.270.1850.099

184281281281238162

356367367324248162

475475475356259173

583583454346238130


R717 (NH3)





20 30 40 50 20 30 40 50

Refrige-rant

Suction temp. ts after temperature

reduction°C

tc = 20°C and 30°C tc = 40°C and 50°C

Suction temperature reduction ∆ts K

1 2 3 4 1 2 3 4

R717 (NH3)

+100

−10−20−30−40

0.40.50.50.40.30.2

0.80.80.80.60.60.6

0.91.01.00.80.80.8

1.01.01.01.01.01.0

0.50.40.40.40.40.2

0.80.70.60.60.60.6

1.00.90.80.80.80.8

1.01.01.01.01.01.0



Design/Function

PMC 1 PMC 3

1. Valve body1a and 1b. Channels in valve body10. Regulating spindle11. Throttling cone 12. Valve seat22. Locking ring24. Servo piston24 a. Equalizing hole in servo piston30. Bottom cover36. Plug40. Cover40 a, b, c and d. Channels in cover44. Blanking plug

for pressure gauge connection60. Manual operating spindle

The PMC regulator is a servo-operated main valve whose function is determined by the pilot valve.The main valve with pilot valve controls refrigerant flow by modulation in accordance with the pilot valve impulse.The degree of opening of the PMC is determined by the pressure difference (differential pressure) between pressure p2, which acts on the top of the servo piston (24), and pressure p3, which acts on the underside of the servo piston.Because of the channel (1b) in the valve body, pressure p3 acting on the underside of the servo piston (24) is equal to the regulator discharge pressure, p4.If this pressure difference is 0, the regulator will be fully closed.If the pressure difference is approximately 0.7 bar or more, the regulator will be fully open.At pressure differences (p2 - p4) between approximately 0.3 bar and 0.7 bar the opening degree of the regulator will be correspondingly proportional. The shape of the throttling hole (11) gives an ideal regulation characteristic to servo-operated regulators.

The degree of opening of the regulator is thus controlled by applying a pressure, p2, on the top of the servo piston which is equal to or greater than the discharge pressure, p4.p2 = p4 ∼ closed position.p2 = p4 + 0.7 bar ∼ completely open position.p4 ≤ p2 ≤ p4 + 0.7 bar ∼ proportional degree of opening. The maximum pressure, p2, that can be built up on the top of the servo piston (24) normally corresponds to the pressure, p1, acting on the regulator inlet side. Inlet pressure p1 is led, via the drilled channels (1a, 40a, 40b, 40c, 40d) in the valve body (1) and cover (40) through the individual pilot valves and on the top of the servo piston (24).The degree of opening of the individual pilot valves determines the size of pressure p2 and thus the degree of opening of the regulator, i.e. the equalisation hole (24a) in the servo piston (24) ensures that pressure p2 is balanced in accordance with the degree of opening of the pilot valve.



DesignFunction(continued)

CVC

Blanking plug A + B

Blanking plug A

43. Gasket 44. Blanking plug for

pressure gauge connection 81. Gasket 82. O-ring103. Banjo fitting104. O-ring105. Protective cap106. O-ring107. Signal connection108. Pilot orifice109. Banjo fitting connector 110. Diaphragm111. Spring112. Setting spindle

EVM

1. Coil 2. Armature 3. Armature tube 4. Gasket 5. O-ring 6. Seal ring 7. Spacing ring 8. Nut 9. Locking knob10. Union nut11. Valve seat

PMC opens when the pressure ps in the signal connection (107) is below set point.The PMC 3 has three connections for pilot valves, two in series (marked "SI" and "SII") and one in parallel (marked "P").

If only two pilot valves are necessary for the required function, the third pilot port must be blanked with the blanking plug provided. Fitting instructions accompany the blanking plug.



Dimensions and weights

PMC 1 and CVC PMC 3, CVC and EVM

CVC EVM

Pressure gauge connector, self-closing

Pressure gauge connector,¼ NPT

Pressure gauge connector, flare

External pilot connection

Pressure gauge connectorPressure gauge connector,cutting ring connection

Type Size H1 H2 H3 H4 H5 H6 H7 L L1

L5 max.B1 B3

Weight with flanges but without pilot valves

10 W 20 W PMC 1 PMC 3 Flangeset

PMC 15 - 20

mm mm mm mm mm mm mm mm mm mm mm mm mm kg kg kg

PMC 3 66 162 79 101 178 117 228 177 106 122 132 75 87 6.5 7.0 1.1

Pilot valvetype

Weightkg

CVCEVM

0.70.5

Size A B L M

6 mm 19 14 39 27

10 mm 19 19 40 29

RD4ED502

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