Frequently Asked Questions | Dry Coolers Inc.

Dry Coolers Inc.

Industrial Process Cooling Systems

Dry Coolers, Inc.
575 South Glaspie Street
Oxford, MI 48371 USA


Frequently Asked Questions

Many of our most common questions are answered below. If your question is not answered below and is general in nature please email or call us.

If you have a specific technical question about one of our products, please use the Ask A Technical Question form to get in touch with us

Most closed-loop water systems use a sodium nitrite based inhibitor and a biocide to prevent biological contamination. These inhibitors will protect both the ferrous and non-ferrous materials in your piping system. Vendors can supply the inhibitor with a colorant, which allows the treatment to be visually monitored.

Because evaporative towers scrub the air that passes through them, they are prone to collecting debris from the air. This debris can accumulate and cause flow restrictions; as well as aggravate corrosion. Also, after the water evaporates, dissolved minerals are left behind and accumulate rapidly. For these reasons, a properly engineered and administered water treatment program must be employed continuously with the cooling tower.

In an open tower cooling system, the water quality must be regularly monitored and treated to control the following conditions:

  1. Lime scale and other water mineral deposits
  2. Corrosion of all types
  3. Micro-biological growth, such as algae, bacteria, fungus and molds
  4. Suspended solids accumulations, such as airborne dirt and debris that is washed into the cooling tower water.

Dry Coolers recommends consulting a local water treatment supplier (Calgon, Nalco, Culligan, etc.) that is familiar with your local water quality to monitor your treatment program.

Closed-loop systems are less susceptible to corrosive agents than Open Tower systems. For this reason they are often left untreated.

However, closed-loop systems must have corrosion protection. An untreated closed-loop water system can cause serious corrosion in your equipment.

While the system is running, vent the high points in the process discharge piping to remove air from the pipe. Most problems with the initial start-up are associated with filling the system and releasing air out of the process piping.

If it sounds like there are marbles in your pump, it is more then likely caused by cavitation, or air getting into the pump. Both of these problems will severely shorten the life of the pump impeller, and should be corrected immediately.

We will be posting an article on troubleshooting these problems shortly.

Typically, the piping should be sized large enough so that frictional pressure drop within the piping system make up less than 10% of the operating pressure of the system. For example, a system operating at 100 psi should have less than 10 psi of frictional pressure losses in the piping system. Pressure losses in a piping system can be readily determined using the "equivalent length" method that is found in most piping handbooks. Since most piping systems are not complex, we have provided a simple table to use as a rule of thumb for sizing the piping. Use this table for systems requiring less than 200’ length of pipe (less than 30’ for gravity drain) and that have a minimum number of valves and bends.

Larger and more complex systems may need special consideration. Consult Dry Coolers for recommendations.

Example: A 150 gpm Vacuum Furnace Cooling System with a plate & frame heat exchanger and a cooling tower. This type of loop has closed-loop process piping and open loop cooling tower piping.

Assume 150 gpm for both loops:

Section of Pipe Minimum Pipe Diameter
Process supply piping to the furnace 3"
Process return piping (from the furnace to the tank) 4"
Cooling tower supply pipe 3"
Cooling tower gravity drain to remote sump tank 5"


Pipe Diameter (in) Max. Supply Piping Flow Rate Max. Return Piping Flow Rate for Furnaces (1) Max. Gravity Return Flow for Remote Towers (2)
1 10 6 2
1.5 35 20 9
2 75 40 22
2.5 120 70 40
3 200 120 63
4 350 250 135
5 550 450 247
6 800 750 400
8 1500 1500 865
10 2500 2500 1570
12 4000 4000 2540

(1) Typically, the back pressure on a furnace must be minimized. The return water piping for a furnace is usually one size larger than the supply pipe. For example, if a furnace requires a 3" supply, then a 4" return is used.

(2) The gravity drain flow returning from a cooling tower is based on a minimum pipe slope of 1/2" / ft with the pipe 3/4 full of water. Based on Manning Formula, n = 0.015. The length of the gravity drain pipe should be kept to a minimum to prevent overflowing the indoor tank and prevent water from backing up in the tower basin.

It is often necessary to determine the volume of water held in a cooling system so that appropriate concentrations of corrosion inhibitor and/or glycol can be added.

The volume of water in your system is determined by adding the volume of water in your pipes, tanks, cooling equipment, and your process equipment. At your request, Dry Coolers can provide the cooling equipment volumes.

The following table may be used as a guide for determining the volume within pipes.

1" 4.5
1.5" 10.6
2" 17
2.5" 25
3" 38
4" 66
5" 104
6" 147
8" 260
10" 410
12" 587


Volume in Piping
Volume in Taks
Volume in Equipment

Sources of Ethylene and Propylene Glycol Based Anti-Freeze as of 11/21/01.

Supplier Phone Propylene Glycol Ethylene Glycol
Dow Chemical 800-447-4369 DowFrost Dowtherm
Houghton Chemical Co. 617-254-1010 Safe-T-Therm Wintrex
Interstate Chemical Co. 800-422-2436 Intercool NFP Intercool NFE
Huntsman Petrochemical 713-235-6000 Jeffcool P155 Jeffcool E105
Noble Company 800-678-6625 NoBurst-100 None
DOW/Union Carbide 800-331-6451 Ucar Protherm UcarTherm
    Norkool TriTherm


Many of the present uses for ethylene glycol are based on its properties as a freezing point depressant, but this compound is also valuable in numerous applications which depend upon one or more additional properties. The ease with which it reacts with other chemical intermediates plus its solvent, lubricant, plasticizing, and hygroscopic properties-all are likewise responsible for its popularity as an industrial raw material.


Propylene glycol is unique among the glycols in that its very low toxicity permits it to be taken internally. Because of this fact there are grades intended for industrial use and those intended for applications that may involve absorption into the human body. In common with the other glycols, propylene glycol is odorless and colorless and has a wide range of solvency for organic materials, plus being completely water soluble.

Freeze Protection requires a glycol concentration level sufficient to prevent the formation of ice crystals at the lowest temperature experienced by the fluid. Freeze protection is imperative when the system requires pumping.

Burst Protection only requires a glycol concentration high enough to prevent bursting and other mechanical damage from freezing, but not necessarily high enough to keep the fluid pumpable. Burst protection requires less glycol than freeze protection and is suitable for chilled water systems that are dormant in the winter. As the temperature drops below the freezing point of the fluid in a system with burst protection, ice crystals begin to form and the solution becomes a slush. The fluid expands as ice is formed. This mixture may or may not be pumpable, but it is fluid enough so that the excess volume flows into an expansion tank without damage to the system. As the temperature drops further and all the water freezes, the glycol will begin to freeze and contract.

For freeze protection, the required concentration of inhibited glycol fluid in a system depends on the operating conditions of the system and the lowest expected ambient temperature. For corrosion protection, it’s also important to consider the materials of construction, the age of the system and other variables. Your local glycol supplier representative can help you analyze the specific requirements for your system.

The table below shows the protection from freeze damage provided by various concentrations of DOWFROST glycol inhibited fluids. To determine the concentration required, select the lowest expected ambient temperature and decide whether the cooling system requires freeze protection to keep it pumpable, or burst protection to simply prevent damage from fluid expansion.

As a further measure of protection against dilution error, or unexpected cold temperatures, select a temperature that is at least 5°F colder than the lowest expected ambient temperature. If, for example, the lowest expected temperature is -15°F, select the line in the table below for -20°F. The table shows that at this temperature, a solution of 45% DOWFROST is required for freeze protection. A concentration of 30% to provide burst protection at this temperature.


  Freeze Protection Burst Protection
20 17% 11%
10 26% 18%
0 34% 23%
-10 41% 28%
-20 45% 30%
-30 49% 33%
-40 51% 35%
-50 53% 35%
-60 55% 35%

The fan on a cooling tower draws in thousands of cubic feet per minute of outside air that contains sand, dust, insects, and fibers from vegetation. These airborne contaminants mix with the process cooling water and eventually these suspended particles find their way into heat transfer surfaces. After a period of time these surfaces become fouled and insulated causing equipment to run hotter and replacement or repair is necessary.

By removing 98% of these suspended solids mechanically, fouling is greatly reduced and chemical water treatment and bleed from the system can be reduced significantly.

Full stream filtration protects the system from dirt deposits such as winds blowing over newly plowed fields, chunks of scale eroding from steel pipe or foreign deposits encountered by adding new piping to an existing system.

By utilizing an optional purge receptacle, expensive treated process water is not wasted in the purge cycle. A small continuous flow of dirt laden process water removed by the separator is filtered and contained in the receptacle while the clean water is returned to the cooling system. The receptacle can then be isolated for easy contaminant removal without interrupting the process water flow and zero discharge to the sewer.

The key to good filtration is to provide a system where the dirt laden water can enter the suction of the pump that discharges into the CyClean separator for maximum filtration of the system. If the solids can be kept in suspension, they will eventually enter the suction of the pump and then be filtered by the separator before they foul your equipment.

Calgon CorSTAT 20
NuCalgon Ty-Ion B20
Chemco 4364

Consult with the supplier relative to your specific needs.