Control Of Cooling Water; Quantity And Pressure Of Cooling Water; Cooling Water Quality - Hitachi NEXT Series Instruction Manual

8. STANDARD COMPONENTS AND SUBSYSTEMS [Cooling Water]
8.3 Cooling Water

1. Cooling Water Quality

If a cooling tower (open-type circulatory cooling water
system) supplies the cooling water to the Air
compressor, problems such as corrosion, scale, and
slime may be caused by:
(1) higher mineral content due to concentration,
(2) contamination by foreign matter like insects, and/or
(3) production of algae or bacterium. Using the best
quality cooling water is highly recommended.
(4) Refer to the table "Cooling Water Quality" below for
the open type circulatory system.
① Stop the cooling water flow, when the air compressor
has stopped. Open the petcock and the water drain
valve to drain the cooling water (see Figure 1 below).
Failure to perform step 1, can lead to the following:
■ Cooling Water Quality
No
°F(
pH [at 77 25℃） ]
1
2
Electrical Conductance [at 77
3
Chloride Ion Cl ー (mgCl ー
4
Sulfuric Acid Ion SO 2ー (mgSO
4
5
Acid Consumption [at pH 4.8] (mgCaCO
6
Total Hardness (mgCaCO
7
Calcium Hardness (mgCaCO
8
Ferrous Substance (mgFe/ℓ)
9
Sulphur Ion S 2ー (mgS 2ー
10
Ammonium Ion NH (mgNH
4
11
Ionizing Silica SiO (mgSiO
2
12
Isolated Carbonic Acid CO
13
Nitric Acid Ion NO ー (mgNO
3
14
Organic Substance (KMnO
15
Turbidity (mg/ℓ)
Notes: 1. System Water is the one that passes through a heat exchanger of circulatory or qnon-circulatory system.
Make-up Water is the one that is supplied to a cooling tower.
2. Above No. 1, 2, 4, 5, 7〜12 are based on the standard: JRA-GL-02-1994.JRA: (Japan Refrigeration and Air Conditioning Industry Association)
3. The above criteria does NOT give any assurance of trouble-free or problem-free conditions due to other and time-depending factors but the minimum
requirement.

■ Quantity and Pressure of Cooling Water

Item
Max. inlet temp.
Total flow rate
Min. pressure differential (between inlet and outlet)
Temp. differential (between inlet and outlet)
Required water pressure
66
Water-Cooled
Water Relief Pet Cock
Water Drain Valve
Item
°F(
25℃） ] (ms/m)
/ liter)
2ー /ℓ)
4
/ℓ)
3
/ℓ)
3
/ℓ)
3
/ℓ)
/ℓ)
+
4
/ liter)
2
(mgCO /ℓ)
2 2
ー /ℓ)
3
Consumption) (mg/ℓ)
4
gpm (liter/min)
a) The cooling water pipe could freeze and burst in
cold temperatures.
b) The airend case can be overcooled and develop
moisture internally; thus leading to scaling in the
cooling water jackets.
② Clean the cooling water subsystem (cooling water
jackets of the first- and second-stage airends,
intercooler, aftercooler, and oil cooler) periodically.

2. Control of Cooling Water

The service life of the cooling water system depends on
water quality. If the cooling water quality is not within
specification, the cooler pipes can corrode or scaling can
occur. To avoid the problem, periodically sample the
cooling water used and subject it to a quality inspection.
3. Quantity and Pressure of Cooling Water
Refer to the table "Quantity and Pressure of Cooling
Water" below.
Performance of the coolers varies depending
on the extent of throttling the stop valves at
the cooling water inlet and outlet.
To control the cooling water flow rate, throttle
the stop valve at the outlet and leave the stop
valve at the inlet opened completely.
Make-up Water System Water Used
6.0 to 8.0
less than 30 less than 80
less than 50 less than 200
less than 50 less than 200
less than 50 less than 100
less than 70 less than 200
less than 50 less than 150
less than 0.3 less than 1.0
Not detected Not detected
less than 0.1 less than 1.0
less than 30 less than 50
less than 4
less than 0.5 less than 0.5
less than 10 less than 10
less than 10 less than 10
Model DSP-90W6N
DSP-90VW6N
°F (℃)
42 (160)
psi (MPa)
°F (℃)
psi (MPa)
CAUTION
Problem
Corrosion
○
6.5 to 8.0
○
○
○
−
−
−
○
○
○
−
less than 4 ○
○
○
○
DSP-110W6N
DSP-110VW6N
95 (35)
48 (180)
22 (0.15)
16 (9)
22 - 71 (0.15 - 0.49)
Scale
○
○
−
−
○
○
○
○
−
−
○
−
−
○
○