What is a tundish?
A tundish, for sealed heating (boilers) and hot water systems, is a device that allows water released from a PRV discharge, due to an over pressure or over temperature in the system, to be passed from an upstream pipe to a downstream pipe but allows the user to see the water passing, via an open sided design.
It normally consists of an inlet, connected to the body of the tundish, via an open-sided construction (normally by the use of two arms) and then has an outlet which connects into the downstream waste pipework.
What does a tundish do?
On all sealed heating and hot water systems, it is a mandatory requirement that any water passing from the safety device (called a pressure relief valve or PRV) on the system, is conveyed to a place where any passing water can be observed, but that it is discharged safely, not causing any potential danger to persons in or about the building.
The standard tundish provides an industry acceptable way of allowing this water to be observed from the inside of the dwelling, it gives the occupiers a way of seeing this water as a warning that there is something wrong with the system (water does not under normal operating conditions, pass out of the PRV).
However, although it can be seen safely, it still needs to be conveyed to a point of discharge outside or, in the alternative, to a local drain.
If the installer has, for example, a landlocked application (e.g. a vented cylinder being replaced with a combi boiler in the old airing cupboard) or in a high-rise application, getting to a point of discharge other than to internal drain can be really problematic.
A standard tundish does not prevent smells coming back up from the drain. This is why I, invented an open-sided tundish trap with a non-return valve.
What is a dry trap tundish?
The hotun dry trap tundish does what a standard tundish does plus it also stops smells or odours and foul gasses from entering the building via the drain connection.
Because, for instance, a boiler PRV discharge pipe does not run with water that often, a traditional wet trap cannot be used in this application as it may dry out and allow gasses to enter into the building from the waste pipe.
The hotun tundish has a familiar design to that of standard tundishes, in that the inlet is connected to the body in an open-sided manner via two arms, but within the body of the tundish, it has a patented, one-way sprung valve as part of its construction.
The tundish non return valve is held in position by a light spring, strong enough to be held shut against gasses, but light enough to open when there is a small quantity of water sitting above the valve, at which point the valve spring opens and the water passes into the lower waste pipe and then closes again.
What does the hotun dry trap tundish do?
The hotun tundish non-return valve is designed to open (or trigger) at between 5ml and 30ml of water, this equates to a level of the valve aperture and the middle of the (3) tundish valve support arms.
The trigger point is the same for both a boiler tundish and/or an unvented water heater tundish.
Therefore, small quantities of water dripping into the tundish are held in place by the valve until such times the water builds to sufficient quantity. Because of hotun’s open-sided construction, this water can easily be seen by the building occupier, who can then take remedial action and, calling in their local plumber, can then determine the cause of the fault and thereafter fix the boiler or unvented cylinder.
On large, unvented hot water cylinders (above 15 litres in capacity) it is a requirement that they come manufactured with a device that prevents the water in the cylinder to be heated above 95DegC. They achieve this by combining a pressure relief valve with a temperature relief valve or a T/PRV. This valve is designed to open under pressure (to relieve the pressure safely and slowly) or when the water in the cylinder reaches 90DegC. If the temperature in the cylinder starts to climb higher the valve then opens more and is fully open at 95DegC.
At this point, a large quantity of water can be being discharged and the tundish and downstream pipework must be designed to handle this volume of water at very high temperature without being compromised by the heat.
This is why RA Tech UK Ltd, specifically advise on the IM’s that only pipework suitable for this application should be used. As we do not manufacture waste pipework, we do give guidance as to acceptable standards, such as polypropylene (PP), Modified Plasticized Polyvinyl Chloride (MuPVC) High-Density Poly Ethylene (HDPE) and be correctly supported.
It is important to remember that the volumes discharged by a PRV are totally different to that discharged by a TRV, the former with only drips being released and the latter potentially high volumes, so the correct configuration of pipework leading up to the tundish and away from the tundish are vital parts of the system for the installer to get correct to allow for the successful discharge of water released.
Service/Maintenance of the hotun dry trap tundish
It is best practice to service boilers or unvented cylinders once a year. At this point, an installer should check the hotun for its correct operation and can also observe and report on any suspect historical discharges.
On unvented hot water heaters, this can be observed as slight water residue on the plastic, or (in hard water areas) a small build-up of limescale. With hotun, this limescale can be easily cleaned off by pulling the valve up through the valve aperture (which then self cleans any deposits off), wiped with a finger/cloth and then harmlessly pushed back into position, without having to dismantle any part of the product or remove it from the pipeline (unlike some other products) saving the installer time and money on this aspect of servicing work.
At the same time, the installer can feel for the valve’s smooth and unobstructed movement, proving correct operation and should pour a small quantity of water manually into the tundish to check for the correct trigger point operation.
About hotun and RA Tech UK Ltd
hotun is a revolutionary dry trap tundish. RA Tech UK has pioneered and is market leader, in the removal of T/PRV waste water to drain bringing, for the first time, boiler manufacturers to accept this type of installation, saving installers and contractors, time and money and, sometimes, on large high rise multi-apartment buildings, thousands of ££’s.
For your project or development choose the hotun tundish, plumbing at its best – it’s not just a tundish.
To find out more for boiler applications please click here
To buy one of our hotun dry trap tundishes or products please see our trade suppliers list here
hotun was designed and invented by Russell Armstrong, a professional plumber and Managing Director or RA Tech UK Ltd