How to adjust the Vi setting

 Never perform Vi adjustments while the compressor is in operation. Perform Vi adjustments only after stopping the compressor. Because the rotary shafts are near the Vi adjustment location, there is an increased risk of personal injury or death as clothing can be caught in rotating shafts or tools may get in touch with them.

Numbers enclosed in [ ] in following instructions means the part number in Section 7.1 "Development Views and Sectional Views" and Section 7.2 "Parts Configuration Table" in this manual Chapter 7.

a) First, determine the expected operating condition of the system and work out the Vi value under the condition thus determined (use the formula shown in Section 2.4.3.3 “Why the Vi Needs to Be Changed?” for the calculation) in this manual Chapter 2.

Next, select the L, M, or H port setting, whichever is the closest to the calculated Vi value. The

SCV-series Screw Compressor 4.1 Adjustment of Vi 4-2

b) From the table 4-1 “Number of Turns of Vi Adjusting Rod for Individual Models”, determine how many turns the adjusting rod [444] should be rotated in order to set to the port selected in Step a) above.

Table 4-1 Number of Turns of Vi Adjusting Rod for Individual Models (The unit of "Displacement distance" is "mm".)

From H port to M port From H port to L port

- 160VL 160VM 160VS - 160VL 160VM 160VS Displacement distance - 27 23 18 Displacement distance - 55 45 37 Number of turns of rod - 10.8 9.2 7.2 Number of turns of rod - 22 18 14.8

- 200VL 200VM 200VS - 200VL 200VM 200VS Displacement distance - 34 28 23 Displacement distance - 69 57 46 Number of turns of rod - 9.7 8.0 6.6 Number of turns of rod - 19.7 16.3 13.1

250VLL 250VL 259VM 250VS 250VLL 250VL 250VM 250VS Displacement distance 52 43 36.5 29 Displacement distance 使用

不可

87 72.5 58 Number of turns of rod 13 10.8 9.1 7.3 Number of turns of rod 21.8 18.1 14.5

- 320VL 320VM 320VS - 320VL 320VM 320VS Displacement distance - 47 50 59 Displacement distance - 105 98 98 Number of turns of rod - 10 11 13 Number of turns of rod - 23 21.5 21.5 Note 1: Prior consultation to MAYEKAWA is necessary prerequisite as mentioned in in the

previous page when the port is changed from H port to L port.

Note 2: The travel distance and the rotation number of "From H port to M port" on 320V* have different tendency of change compared with those of other types. The reason can be found in design difference of variable Vi auxiliary slide valve.

Note 3: If the evaporating temperature of your system exceeds 0°C under the L port condition, select a grooved slide valve for the compressor.

In addition, note that grooved slide valve is available to even less than 0°C evaporating temperature under the L port condition.

Table 4-2 Screw Thread Specifications of Vi Adjusting Rod

160V** 200V** 250V** 320V*D

M20×P2.5 M30×P3.5 M36×P3.5 M36×P3.5

Number of turns x Pitch (mm) = Displacement distance of variable Vi auxiliary slide valve

c) If Vi settings are the initial settings before commissioning, set the position of the slide valve at the no load point, that indicates 0% in unloader indicator, by driving the oil pump alone after adjusting the position o% to 100% of the unloader indicator pointer.

If Vi adjusting work is conducted as a change during usual operation, stop the compressor operation after slide valve reaches 0% position.

d) Shut off the electric main power source and control power source of the package unit.

In addition use lockout/tagout to prevent power from being reconnected accidentally during the Vi setting operation.

 Take care to the electric shock accident at the time of conducting the electric power ON/OFF.

e) Remove the domed cap nut [522] at the end of the Vi adjusting rod, then loosen the hexagon nut [453] used as a lock nut. On the compressors produced after March in 2005, a conical spring washer is provided between the hexagon nut and domed cap nut to prevent detachment of the cap nut.

f) Turn the Vi adjusting rod clockwise until it stops.

The position where the rod stops corresponds to the H port position the setting before shipment.

Do not turn the rod any further as applying undue force will break the rotation stopping mechanism.

This position corresponds to that in Sequence (2) in Figure 4-3.

 Do not turn the Vi adjusting rod any further as applying undue force will break the rotation stopping mechanism.

g) Check the inscribed mark (small black point indicated by the white arrow in Figure 4-1) on the Vi adjusting rod, which should be used as a reference point when counting the number of turns of the rod.

h) Turn the Vi adjusting rod counterclockwise by the number of turns determined in step (3). The Vi setting will be changed from the H port setting to the M port setting as shown in Sequence (3) in Figure 4-3.

i) While holding the Vi adjusting rod against rotation, lock the rod by tightening the lock nut.

j) Install the domed cap nut to the end of the Vi adjusting rod and tighten it. Do not fail to install the conical spring washer between the hexagon nut and domed cap nut to prevent detachment of the cap nut due to vibration, or like.

Figure 4-2 Conical Spring Washer

k) By releasing lockout/tagout of the electric power breaker temporarily, and then turn on the control power and the oil pump power.

m) Supply oil pressure to increase the capacity control by individual oil pump operation until the slide valve stops at the full loaded position.

n) If the pointer of the unloader indicator aligns with the 100 % graduation for the port in question on the dial, the Vi is correctly adjusted to that port. This is the Sequence (4) in Figure 4-3.

The M and H graduation marks are rather large in width.

This is because there is a slight difference in indication of the M and H positions among the 13 compressor models, i.e. 160S/M/L, 200S/M/L, 250S/M/L/LL, and 320S/M/L, due to difference in rotor length. The setting may be considered correct if the needle pointer indicates any point in the

Figure 4-1 Vi Adjusting Rod

SCV-series Screw Compressor 4.1 Adjustment of Vi 4-4

Figure 4-3 Vi Changing Sequence from H port to M port