“The Temperature and Pressure Safety Valve” or the “T&P valve” or the “TP valve” or the “Safety valve” are all colloquial terms plumbers use for the same valve.
By: Karel Deist — SABS
We will be discussing the following headings:
• Why is it so important?
• How does it work?
• How is it tested by sabs for compliance to sans 198?
• How must it be installed?
• The plumber’s predicament
Why is it so important?
To answer the first question, we just need to look at the South Africa national introduction in the safety standard for geysers, SANS 60335-2-21: which says in short that in South Africa, certain specific requirements exist regarding the manufacture and the installation of household electric storage water heaters. During the early 1980’s, serious damage to property and loss of life were experienced owing to the actual explosion of household electric storage water heaters.
The South African Bureau of Standards, being the local controller of the relevant standards and the certification of the products, was under obligation to investigate the problem and develop a suitable solution. After extensive investigation, it was found that the problem was caused by a combination of a number of local practical and environmental conditions, for example extreme temperature variations, water quality variation, extensive water mains pressure variations, and a lack of effective installation maintenance.
The solution was the development of a pressure and temperature control safety valve, and the fitting of this valve onto the container in a specific position and manner. The performance of this valve is contained in SANS 198, Functional control valves and safety valves for domestic hot and cold water supply systems. The problem was solved immediately, and consequently this system has become mandatory for hot and cold water supply installations.
It was also decided that the effective and safe installation of the water heater together with the associated pressure and functional control valves and plumbing components should be controlled by a suitable standard for installation, which is SANS 10254, The installation, maintenance, replacement and repair of the fixed electric storage water heating systems, and is made compulsory by major water control authorities.
It is therefore no surprise that the South African National Standard for T&P safety valves : SANS 198 “Functional-control valves and Safety Valves for domestic hot and cold water supply systems” is referred to in numerous related mandatory standards, such as SANS 10252-1 “Water supply for buildings”; SANS 10254 “The installation, maintenance, replacement and repair of fixed electric storage water heating systems”; SANS 10106 “The installation, maintenance, repair and replacement of domestic solar water heating systems”; SANS 151 “Fixed electric storage water heaters”; SANS 60335-2-21 “Safety of domestic fixed electric storage water heaters”. So all of these standards cover all aspects of geyser safety including the SANS product performance, marking and testing; the correct installation into the geyser and in the whole hot water system and in the whole building.
In short, closed (unvented) geysers, commonly called “pressure geysers” or “high pressure geysers” have the potential to explode if not installed and maintained correctly and the T&P safety valve is an important part of a series of safety features in all of the standards mentioned above that together make up a safe geyser installation.
A “cistern type” geyser, also known as a “combination” geyser and also an “open outlet type” both have stored hot water in them at atmospheric pressure (reading zero on a pressure gauge), so the water in them physically cannot be heated over 100ºC no matter how much heating energy is applied to it. However, as soon as water is under pressure as in a closed (unvented) geyser, the water can absorb more heat, so-that at 100kPa pressure the temperature can get to 120ºC, at 400kPa it can reach 152ºC and at 600kPa to 165ºC. Any water temperature above atmospheric boiling point, which is 100ºC at sea level, is called “super heated water” which is highly explosive when it flashes into steam, releasing tremendous amounts of energy (refer the previous SABS article in Plumbing Africa of June 2012 “Burst geyser: real threat or inconvenient nuisance?”). What prevents the explosion? A correctly installed T&P safety valve which complies with SANS 198!
HOW DOES IT WORK?
The T&P safety valve has 2 main operating functions (as can be seen from its name). First it opens just before the water temperature in the geyser reaches atmospheric boiling point, and most South African manufacturers set theirs to open at a temperature of about 95ºC. This lets the very hot but not explosive water and steam out of the geyser where it can discharge safely outside of the building, letting the cold water into the geyser to cool things down and so prevent an explosion from happening. It just requires a faulty or damaged or incorrectly installed or incorrectly connected or removed thermostat that does not switch off the power to the electrical element, and the water will just get hotter and hotter…… Or if a solar water heater is connected to the geyser and no-one is using hot water, like during vacation time, and you can’t switch the sun off, the water progressively gets hotter and hotter, day by day…… then the T&P safety valve opens and saves the day, preventing an explosion.
The second function of the T&P safety valve is to relieve “over pressure” failures of the system. This can occur when cross connections are made between high pressure and low pressure zones in the plumbing network. Often it is due to ignorance or carelessness on the part of someone making a connection onto a pipe without first establishing whether it is the correct pipe. Or sometimes it is due to valves like non-return valves, stop-cocks, ball-valves that are illegally fitted between the expansion relief valve and the water heater. Or the fitting of pressure booster pumps of the wrong pressure rating, or causing pressure spikes on start-up or shutdown, or the wrong rated pressure control valve being installed, or NO pressure control valves being installed, or……etc.
That is why it is understandable why the geyser safety standard requires that the geyser MUST be supplied along with the correct T&P safety valve by the manufacturer.
HOW IS IT TESTED BY SABS FOR COMPLIANCE TO SANS 198?
Although SANS covers the performance and testing of Functional Control Valves – which are pressure control valves, expansion control valves and vacuum control valves – as well, we will for the purpose of this article concentrate on the aspects relating to the safety valves only. However the functional control valves also contribute to the overall safety of the installed geyser system in various aspects and the so requirements of the safety valve are linked to their performance as well.
Performance and pressure test. The T&P safety valve performance test includes a hydrostatic leak test and pressure setting test and an endurance test of 10 000 opening and closing cycles. Bear this in mind when some people think that the valve may only open a few times in its installed lifetime. At the end of the test the safety valve’s pressure settings must still be within the prescribed range. Notice the progressive values of the functional control valves’ pressure settings leading up to the settings of the T&P safety valves and the nominal working pressure of the system: first the pressure control valve’s closing pressure is 70% to 80% of working pressure; then the expansion relief valve’s opening pressure is 95% to 100% of working pressure; and finally the T&P safety valve’s opening setting is 150% of working pressure +-10%. This ties in finally with SANS 151 – the geyser performance standard, which requires the geyser tank to be pressure tested to 200% of nominal working pressure. So you can see how they all fit together to make a safe system.
Heat relief rating test. This test uses a minimum 90litre capacity tank fitted with an 18kW heating element, with the T&P safety valve mounted with a minimum of 50mm of water above the probe, with an air space of at least 5 litre above the water level (to generate saturated steam) and with the inlet to the tank closed. Then the thermostat is short circuited and the water is allowed to boil off to the level of the probe and for the hot water and steam to escape through the T&P safety valve for 5 minutes, all the while checking that the pressure developed in the heater does not exceed the working pressure of the T&P safety valve.
Temperature response test. The valve is mounted in a horizontal position in the tank, with the valve submerged in water at working pressure, and with no air entrained in the tank. A temperature recording sensor is mounted at maximum 10mm away from the outer surface of the probe, midway down its length. Then the temperature of the water near the probe is raised at the prescribed rate and the temperature is recorded as soon as water starts to emerge from the outlet. It must be between 93ºC and 98ºC. Then the power supply is disconnected and the water is cooled at the same prescribed rate and the temperature is recorded at the point which the water stops flowing from the valve outlet. It must not go below 70ºC.
Nominal working pressures. These shall be: 75kPa, 100kPa, 200kPa, 300kPa, 400kPa and 600kPa.
Inlet and outlet connections. For T&P safety valves both the inlet and outlet connections shall be at least be a nominal size of 20mm and comply with the requirements of SANS 1109-1.
Other tests. These include tests for dezincification resistance of brass material; tests for discharge flow rates of at least 40 litre/minute; tests for plastic material components to high temperature; torque tests on connections; inspections on prescribed colour codes for the relevant pressure ratings, labeling and marking, etc.
So after SABS have tested the T&P safety valves and certified that they comply with the prescribed and mandatory standard SANS 198 and the other normative SANS standards called up in it, the vital issue of how they must be installed to ensure that the installations are safe moves outside of SABS, into the plumbing and construction industry under the control of the plumber.
HOW MUST IT BE INSTALLED?
I speak to many people in the plumbing industry including importers, manufacturers, suppliers, installers, specifiers, training providers, insurers and my experience judging by the many questions I am asked, is that with a few notable exceptions, it is clear that many of them have not taken the trouble to find out what the correct prescribed and mandated installation requirements for the T&P safety valves are. It is therefore no surprise to me how many horrific installations inspectors are finding on these installations, and then the ridiculous debates that circulate around in the industry chat forums and chain e-mails (and eventually land on my desk for comment), when the standards are perfectly clear, just read them – you have to, they are law! You are the persons responsible to ensure that the installations are done correctly! There are horrifyingly dangerous things being done with solar water heater installations, heat-pump installations and geyser replacements when it is clear that the concern about making money is top priority, with absolutely no concern about the wellfare and safety of the consumers or with the laws that apply to this matter!
Where do you start to find out what is required? You can start for one with SANS 198 which we have been discussing. Do you have a copy? Buy one or come to SABS and read what it says for free, in Annex A, which is normative to the standard. Normative means that it is an intrinsic part of the standard. It has to be complied with as much as the performance requirements that a T&P safety valve must comply with. It is titled: the safe and effective installation of functional-control valves and safety valves that comply with this standard. Its headings are: functional control; safety valve; dangerous activities and their rectification. Should this not be the priority of every supplier and installer?
It requires that the various components of the system shall be installed strictly in accordance with the appropriate details given in SANS 10254. The safe and effective operation of pressurized domestic hot and cold water installations is ensured by the acceptable installation of the various components of the system and the combined influence of the two valve configurations.
The first is the functional control of the system which is established by three types of valve that operate individually or in a specific combined configuration. Each valve has a unique function in respect of the protection and performance of the overall hot water system, and these functions are as follows:
The pressure control valve is installed on the inlet side of the water heater and is intended to reduce the water supply pressure to a pressure appropriate to the working pressure of the water heater.
Secondly, the expansion control valve is installed on the inlet (cold) side of the water heater, between the water heater and the pressure control valve. It is a functional valve that operates at regular intervals that allows the escape of expanded heated water in the water heater. It prevents the pressure of the water heater from exceeding the working pressure and ensures that the stresses in the water heater body never exceed the design limits.
Thirdly, the vacuum relief valves ensure that the system is relieved of any vacuum buildup and resulting problems in the hot water system.
The temperature and pressure safety valve is the next valve configuration that is critical to the safe operation of the water heater. Occasionally, the automatic control function of the water heater thermostat is, intentionally or unintentionally, rendered ineffective (for example, in the case of the removal of fusible links or the sticking of contact points). When this happens, the temperature of the water in the water heater will rise above boiling point and a state of superheated water with develop. This is a very dangerous condition and, to prevent the development of excessive pressure in the water heater, it is fitted with a safety valve, the functions of which are as follows: The first is over-pressure relief and the purpose of this function is to prevent the static hydraulic pressure in the system from increasing beyond certain specific design limits. Some installers incorrectly introduce this valve as an expansion control valve. It is very important that this valve, although it does not protect the system against a faulty expansion control valve, was never considered of designed as a functional valve.
To use this valve as a functional valve will induce excessively high stresses in the water heater tank which could lead to rupture of the tank with consequential flooding and damage.
Secondly, the temperature probe’s function is to cause the valve to open when the temperature of the water in the water heater exceeds the preset temperature. The heated water escapes through the outlet thus allowing cold water to enter through the inlet. A safe condition is maintained until the fully automatic control function has been fixed.
The combination of the above actions ensures the effective and safe performance of the system.
This SANS 198 annex A also deals with dangerous activities and their rectification: In some installations, TP safety valves might not have been installed or not installed correctly and in such cases it is imperative that the system be urgently checked by a qualified plumber and upgraded by correctly fitting a TP safety valve.
Any discharge from the TP safety valve indicates a failure of some component of the system. The valve should not be plugged and the failure should be rectified. The discharge pipe from the TP safety valve should be of metal and of nominal size not less than that of the TP safety valve discharge connection. In general, no valve should ever be tampered with or be readjusted. All valves should be installed and treated only as recommended by the manufacturer.
You will notice that SANS 198 annex A requires that the installation must be done to comply with SANS 10254, which is also mandatory in terms of the Water Services Act regulation R509 of 2001. How must it be installed? Look in SANS 10254 (if you are an installer, you obviously must have a copy) at figures 6 – Closed (unvented) water heater with combined pressure control and expansion control valve, and figure 8 – Closed (unvented) water heater located at a level lower than all outlet points and with combined pressure control and expansion control valve.
Both of these figures show the TP safety valve mounted on the water heater with the caption pointed to the outlet pipe “metal discharge pipe extended to the outside of the building”.
Some other important points in SANS 10254 to bear in mind:
Under point 184.108.40.206 it requires that all components used in assembling shall be of an approved type (in South Africa that means it must comply with the relevant SANS standard) and shall be matched in terms of the pressure rating of the system. This also includes the other various valves like ball valves, gate valves, also pipes and fitting etc.
Under point 220.127.116.11 it makes allowances where some of the provisions of the standard cannot be applied that it must comply with the details in a rational design developed by a professional engineer on acceptable installation drawings, and that the rational design shall not compromise the safety and performance principles incorporated in the standard. That means that even an engineer must comply with principles regarding the discharge pipe of the safety valve for instance that it must discharge outside of the building and that SANS compliant pipes and fitting systems must be used.
Under point 18.104.22.168 it requires that the installation shall comply with the relevant national legislation which includes the Water Services Act, the Occupational Health and Safety Act and the National Building Regulations Act. All of these acts by reference in their regulations make SANS 10254 mandatory. In other words if you do not do the installation strictly according to the standard you are contravening three acts of parliament. As a plumber you are therefore compelled to find out what these laws require of you in connection with geyser installations, replacements, retro-fits, repairs etc. So, if you are a supplier or installer of geysers and geyser components (like T&P safety valves), do YOU know what these laws require of you? If not, should you be a supplier or installer?
Under section 22.214.171.124 it requires that the plumber whom installs/replaces a water heater or does any maintenance or repair work to the water heater installation, even just fixing a leak or a pressure control valve, must first look at the installation and inform the owner or user in writing what aspects of the installation do not comply. The reason is that while the legal responsibility for the safety of the heating system is placed by law on the owner of the property, and who by law must have it fixed, it is also the legal responsibility of the plumber to inform the owner – in writing. Are you, the installer/repairer/replacer doing this? On every geyser or geyser valve related job? From the complaints SABS are getting, it would appear that very few of you are.
How else will the owner know that it must be fixed? The other mystifying thing is that it would most likely lead to you getting more work and earning more money, so there is added motivation for you to do it, besides your legal responsibility.
Under 4.3.5 it refers to solar water heating and heat pump retro-fit installations that connect to existing water heaters, which can change a safe installation into an unsafe one. Often safety components like thermostats and TP safety valves are moved or removed in an attempt to fit thermal sensors and flow and return pipes to the water heaters and this is both dangerous and it invalidates the warranty of the water heater and other critical system components. Such modifications are not allowed in terms of this requirement. I wonder how many plumbers who install heat pumps and solar water heaters have given this thought. It includes suppliers of these units that have installation instructions that do not comply with the prescribed standards, or “training providers” that incorrectly “train” installers.
Under 5.2 various requirements for the discharge pipes from valves are required, for instance that the discharge pipe from TP safety valve shall always be of metal and shall be at least the same nominal size as the valve outlet, which would be either copper SANS 460 size 22mm, or 22mm stainless steel pipe or 20mm NB SANS 62-1 hot dipped galvanized medium pipe. If the total length is longer than 4m with not more than 3 bends (either a long radius galvanized wrought steel 90° bend complying with SANS 62-2, or a SANS 460 class 1 or 2 formed 90° bend or a 45° capillary elbow), and the length reduced by 600mm for every extra bend (other than the 3 allowed), then the total pipe length shall be increased in size (22mm copper/stainless steel up to 28mm, or 20mm NB galvanized medium up to 25mm NB) to a total length of 9m, shortened by 600mm for every bend in access of the 3 allowed.
The pipe must also incline downward continuously from the valve outlet, to discharge outside the building so as to ensure the drainage of both the valve and piping and so that any discharge can be readily observed with the minimum risk of injury or damage due to steam or hot water. Blockage due to freezing must also be prevented and the pipe-work shall not cause water traps to develop which could prevent the free return of air into the system. The T&P safety valve discharge pipe must also never be joined together with the expansion relief valve discharge pipe and each must discharge at a point which is visible outside the building and in a position where the discharge from the pipe will not case a nuisance or inconvenience to the occupants or damage to the building.
Altogether that relates to more than 10 different requirements to one section of pipe! Clearly from a safety point of view, this T&P safety valve pipe is the most important pipe in the building, and every one of these requirements ARE LAW!
THE PLUMBER’S PREDICAMENT
Plumbers who are doing solar installations, heat-pump installations and insurance geyser replacements, because they are often dictated to by their contract terms of reference, or performance/service level agreements, or product-specific training and installation instructions, or sales deals over which they have no control which don’t include the required rectification, or prescribed financial payment per job card, etc., which all pressurizes them to break the mandatory safety requirements or to not be in a time or payment position that allows them to do the required rectification. Their dilemma therefore is that if they don’t do what the controlling business employers say, or try to point out their predicament, they will likely lose their livelihood. These primary employers or their agents appear to have an attitude something like this: “We just remove them from our list of installers, there are hundreds more who will step into their place.” This is an untenable situation and is happening on a frighteningly large scale in the industry.
Such issues include using substandard pipes and fittings on T&P safety valve outlets; not quoting on and correcting existing unsafe T&P safety valve installations that solar and heat pump retrofits are being connected to; doing unsafe changes to T&P safety valve installations; claiming rebates on installations that are unsafe and non-compliant; using non-compliant geysers and T&P safety valves, and so on.
One really scary situation is the illegal use on the outlets of T&P safety valves of very thin walled light steel pipe, of undersized nominal size, that does not comply with the very clear requirements for steel water pipes in SANS 10252-1 (section 5.2.5), using inappropriate connection fittings that have built in corrosion cells (where 2 different metals are in contact) in the joints etc. and in spite of all the clarity in all the standards that relate to it, the lawbreakers are undermining the law by openly promoting uncertainty by going around asking “Do you really think it is unsafe to use this illegal pipe and fittings” as if the requirement is unclear or incorrect. It is as if asking: Do you really think it is unsafe to….not wear safety belts; not to wear crash helmets on your motorbike; not fit number-plates; not service your vehicle; drive with worn tyres; drive drunk; drive over the speed limit; driving while talking with your cellphone against your ear; etc.
Furthermore these lawbreakers appear to justify their argument by saying: 1 everyone is doing it or; 2 I’ve been doing it for 6 years now and I’ve not had a problem. Or in the case of using the illegal light galvanized pipe, they may say “1 it is cheaper than copper; 2 copper pipe outside the building gets stolen, etc”.
But the point is being missed: 1 it’s against the law; 2 and by doing it yourself and by trying to justify it you are contributing to the worsening general lawlessness in the country; 3 you are doing it with other people’s money; 4 you are not telling the owners that you are doing illegal things to their properties and putting them at risk; 5 you have gotten away with it until now because no-one was policing it; 6 by sanctioning and financially supporting and benefitting from this illegal activity you have influenced lesser ones in the industry who look up to you, to now make using this illegal pipe and fitting combination a standard practice. They are now using this inferior and unlawful piping method as a general water pipe in buildings and on solar waterheating installations and on heat-pump installations! It has gone from bad to worse.
What has further happened is that this illegal market is now being flooded with even more inferior piping material with thinner wall thickness and not even hot dipped galvanized anymore but with only very lightly applied electro plated zinc, with no protection on the weld seams! It has even less corrosion protection than electrical conduit pipe, and is being used on the most critical section of pipe in the whole hot water system which has the most prescriptions than any pipe in any plumbing system. Most installers cannot even tell the difference between electroplated zinc and hot dipped galvanized! The suppliers know the difference, are they less guilty than the installers who buy it from them?
It has been claimed that some municipal officials have given their approval for this illegal practice. If it is true, can you see how far this thing has gotten to? It is against the Constitution of South Africa that no municipal official or bylaw may contradict a National Law, an Act of Parliament. But all of this is just adding to the undermining and negative propaganda that the lawbreakers are engaged in spreading. All because the very clear standards are being ignored!
What is the point of the testing that sabs is doing at their testing laboratories to ensure that the t&p safety valves are performing as they should to protect the south african consumer and public, while the equally or more important, installation standards are not only being ignored but rather willfully contravened by the very industry who claim to protect the health and safety of the consumer and the wastage of water?