Cooling Water - 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:
Water Relief Pet Cock
Water Drain Valve
Cooling Water discharge valve
■ Cooling Water Quality
No
1 pH [at 77°F (25℃)]
2 Electrical Conductance at 77°F (25℃)] (ms/m)
3 Chloride Ion Cl (mgCl
ー
4 Sulfuric Acid Ion SO
2ー
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 (mgS
2ー 2ー
10 Ammonium Ion NH (mgNH
4
11 Ionizing Silica SiO (mgSiO
2
12 Isolated Carbonic Acid CO
13 Nitric Acid Ion NO (mgNO
ー
3
14 Organic Substance (KMnO
15 Turbidity (mg/ℓ)
Notes: 1. Cooling Water is the one that passes through a heat exchanger of circulatory or non-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
74
Water-Cooled
Water Drain Valve
Cooling Water discharge valve
Item
/ liter)
ー
(mgSO /ℓ)
2ー
4
/ℓ)
3
/ℓ)
3
/ℓ)
3
/ℓ)
/ℓ)
+
4
/ liter)
2
(mgCO /ℓ)
2 2
/ℓ)
ー
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 50
less than 50
less than 50
less than 70
less than 50
less than 0.3
Not detected
less than 0.1
less than 30
less than 4
less than 0.5
less than 10
less than 10
Model
DSP-45WTN
℉ (°C)
24 (90)
psi (MPa)
℉ (°C) 13 (7)
psi (MPa)
CAUTION
Problem
Corrosion
6.5 to 8.0
○
less than 80
○
less than 200
○
less than 200
○
less than 100
−
less than 200
−
less than 150
−
less than 1.0
○
Not detected
○
less than 1.0
○
less than 50
−
less than 4
○
less than 0.5
○
less than 10
○
less than 10
○
DSP-55WTN
DSP-55VWTN
95 (35) or less
24 (90)
22 (0.15) or more
14 (8)
22 - 71 (0.15 - 0.49)
Scale
○
○
−
−
○
○
○
○
−
−
○
−
−
○
○
DSP-75WTN
DSP-75VWTN
32 (120)
16 (9)