By Grant Laidlaw
Experiencing problems of a technical nature, drop us a line at firstname.lastname@example.org or email@example.com with problem page in the subject line.
Welcome to the PROBLEM PAGE. We find many people request assistance in the practical aspects of the industry. In response we will investigate the problem and endeavour to present the best possible solution. Thank you for all your questions sent in. Send your problems (and sometimes your creative solutions) to firstname.lastname@example.org or email@example.com with problem page in the subject line. You may include pictures. Andre Henning asks: We hear about injuries associated with refrigerants coming into contact with the skin. When it actually happened nobody knew what to do. What does one actually do should this happen? Andre I hope there were no serious injuries. This is a good question as I have seen that in an emergency situation people are not aware of what procedure to follow and often panic, causing further unnecessary injury. We are dealing with refrigerants with a low boiling point in liquid form. One should always use the correct personal protective equipment (P.P.E) when dealing with refrigerants, remember safety is your responsibility. The recommended P.P.E is: • Safety goggles. • Non absorbent gloves. • Clothing -Overalls that cover torso, arms and legs. The table below gives an idea of some refrigerants liquid temperature coming into contact with the skin at sea level. Refrigerant R22 R134A
Temperature - 40.8°C - 26.2°C
Refrigerant R404A R410A
Temperature - 45°C - 53°C
As the refrigerant comes into contact with the skin evaporation rapidly occurs. The refrigerant requires heat energy to evaporate and in this instance obtains the heat energy for the most part from the skin. A rapid, below freezing, temperature drop causes mild to severe frost bite. Should the liquid refrigerant enter the eyes, eye damage could result. Should an accident occur the following represents the recommended treatment: Inhalation: • Remove patient to fresh air, keep warm and at rest. • Apply artificial respiration if breathing has ceased. • In event of cardiac arrest apply cardiac massage. • Obtain immediate medical assistance.
Liquid refrigerant on skin: • Remove contaminated clothing. • Immediately run cold water over effected areas for at least fifteen minutes. • If irritation or blistering occurs obtain medical attention. Liquid refrigerant in contact with eyes: • Immediately irrigate with cold water, holding the eyelids open for at least ten minutes. • Obtain immediate medical attention. Jan Joubert from Klerksdorp asks: My major bugbear is refrigerant leaks, we often have to go back to repair leaks and I am getting frustrated with the situation and my staff, how can I minimise leaks? Jan, do not feel alone, refrigerant leaks are problematic for most people. Here is a picture of a suction line that I came across to give you an idea.
To quote a colleague of mine “One does not know whether to laugh or cry”. Firstly one must look at the attitude and the ability of the people doing the work. The adage: There is never enough time to do the job correctly the first time but always time to go back may apply to your situation. Does your staff have the ability to correctly size the flare for a flared joint, removing the burrs and identifying cracks? I find that in many cases the fundamental skills are not in place and this may be the root cause of your problem.
The following illustrates the basics of a flared joint:
Look for: Size, is the flare large enough to mate with the angled sealing surface on the fitting but small enough to pass easily through the flare nut? Burrs, the internal burr must be removed as a burr will prevent the correct seating of the flare. Cracks, at times the copper pipe may crack when flared a drop of refrigerant oil on the angled surface of the flaring tool may help prevent cracks from developing.
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Pipe diameter reduced by over tightening of cutter and with internal burr.
Correct use of cutter with internal burr.
Burr removed prior to flaring.
Does your staff have the skills to swage / braze correctly - achieving penetration of the brazing material? It may be of value to your company, both technically and as a team building exercise to have each of your technical staff perform a practice swaged joint. Cut the joints open lengthwise with a hacksaw and check for penetration. The following picture illustrates two joints that have been cut open.
Minimise the length of pipe runs. Use brazed joints in place of flared joints. Ensure correct refrigerant charge. Minimise vibration using vibration absorbers and vibration coils. Secure piping. Minimise excessive operating pressures. (For example, high head pressures due to dirty condensers) Leak test at regular intervals. Monitor refrigerant usage.
Stanley Lekwane writes Thank you for your very interesting answers. I am mainly in the domestic fridge / freezer repair side of things. I have noticed that in some cases the capillary tube is wound around the suction pipe. Could this be an answer to just dealing with the extra length but in some cases the capillary is soldered to and even put inside the suction line right up to the evaporator. My question is why all this effort? Most people I encounter do not notice this detail. Stanley the reason for the effort is heat exchange. Heat exchangers of this type are normally used in small compact units but can be purchased for larger commercial units.
A commercial heat exchanger
As the name indicates, they provide for heat transfer from the warmer liquid line to the cool gas in the suction line. The liquid refrigerant flowing to the evaporator or thermostatic expansion valve is therefore sub-cooled and superheat is added to the cool suction gas. As you know the smaller domestic units have a capillary tube for a refrigerant control. The capillary tube is wrapped around, soldered onto, or run inside the suction pipe from near the compressor to near the evaporator for heat exchange. The advantages of having the heat exchanger at little or no extra cost are:
The left hand joint has good penetration. The right hand joint has insufficient penetration and some oxidisation is present as nitrogen was not used to purge the pipes. The joint on the right is mechanically weaker and when subjected to stress or vibration may work loose or crack resulting in a refrigerant leak. In addition, should the right hand side joint be on the suction line of a low temp application, any moisture in the system may enter the gap in the joint via capillary action. As the unit cycles the suction line temperature fluctuates between negative and positive degree Celsius. This causes the moisture to expand and contract on each cycle, gradually forcing open the joint unit a refrigerant leak is formed. (Think of a bottle of cold drink in a freezer) In addition to the above the following represents good practice for minimizing refrigerant leaks: •
Minimise the number of joints.(Use a pipe bender)
Increasing the heat of the suction gas is advantageous in that it tends to evaporate any liquid passing into the suction line, thus adding some protection to the compressor against “flooding back”. By sub-cooling the liquid refrigerant it can absorb more latent heat as it changes into a gas. A heat exchanger, therefore, also increases the efficiency of the system. REFERENCES: ACRICSA Thanks to all for writing in with interesting questions. Looking forward to hearing from you – Grant Laidlaw