Please read the result of my typing efforts at home in the last 4 days, copied and pasted here:
Conversion of Premier Padmini to run on a degassing tank equipped cooling system:
Why this need? – The original non-AC car is fitted with a pressurized (7 psi, upgraded to 11 psi) 3 row 75 tubes equipped vertical flow radiator assisted by a centrifugal water pump and an axial flow fan. The water pump has a design mass flow rate of 54 lpm (liters per minute). The fin density is around 10 fins per 25 mm of radiator vertical dimension. This system is very well capable of handing the engine’s cooling needs with good margin. The TD or "Delta T" as it is normally known hovers in the region of around 50 to 55 degrees C. Delta T is the difference in the temperature of coolant at it’s outlet point of the engine to ambient temperature measured under a standardized duty cycle. This is measured in 3 modes on plain road and gradient in GVW condition. However, this system although pressurized is not sealed. This means that as the coolant expands when heated, the additional volume will escape through the pressure valve of the radiator cap to atmosphere and will be lost forever. There are 2 methods to prevent coolant loss in this way. As usual, there is only one correct way. So, what are the two ways? 1 – Use of surge Tank. 2 – Use of degassing Tank. Both systems work. I will first describe both systems in detail and then I will tell you why the degassing tank is vastly superior to the surge tank. I will also provide complete procedure you need to follow to correctly fit your car with a degassing tank. Needless to state, this is an indicative procedure only.
The surge tank – see any Maruti 800 or Zen etc and the plastic bottle you will see there is the surge tank. So, how does it work? To start with, coolant is filled in the radiator as well partially in the surge tank. When the engine runs, coolant will expand. This expanded volume will escape through the pressure valve of the radiator cap into the surge tank. As the coolant surges into it, it is known as "surge tank". When the car is stopped, the coolant temperature drops, its volume reduces and tends to create a partial vacuum in the space that is leftover when the coolant contracted. This is when a small vacuum valve in the radiator cap opens and as its orifice is connected to coolant in the surge tank, coolant rushes back into the radiator against vacuum created there. This is the classical way to replenish the radiator. So, what are the system shortcomings? First, radiator cap’s valves must work perfectly. Going by the nonsense available in most shops, this leaves much to be desired. The radiator cap suitable for surge tank will have two rubber gaskets, one on each side of the outlet connection. If these gaskets do not seal out the atmosphere (specification of the rubber, quality of the rubber, parallelism of the joints, de-burring of the faces etc), atmospheric air will immediately enter the radiator and the surge tank will not operate at all and you will not know also. Second, in the best case scenario, imagine that everything is working perfectly. The surge tank still has a basic deficiency. Imagine a highway drive. Your engine is hot. The coolant has surged out into the surge tank. You stop at a roadside joint for tea for 10 minutes. Imagine what will happen. The coolant temperature drops by around 10 degrees in 14 minutes (it is known). Please note that the coolant temperature has not dropped sufficiently for the coolant to contract and go back to the radiator. The surge tank just cannot do its job. Third, even the best of engines is going to generate some cavitation due to internal cooling system micro-pressure differences and also through the water pump bearings (cavitation means a mix of coolant and air). The result of this cavitation has to settle inside the top tank of the radiator, as it is the topmost point. There is no other place for it to go. As mass flow continues to occur, there are distinct possibilities that this cavitation will be forced into the system again and again and come in contact with the cylinder block and head areas, which must remain free of cavitation for best performance and reliability requirements. This will create micro hot spots, which are not good for the health of the engine. Fourth, when the engine is running, the surge tank remains a passive part of the cooling system. It essentially does nothing. For all practical purposes, you can remove it and still merrily drive the car.
So, in order to overcome all these shortcomings, what to do? Essentially, operate the engine under a wall of coolant. This is exactly what a degassing tank does.
The degassing tank – see any Indica and the plastic bottle you will see there is the degassing tank. So, how does it work? Essentially, the beauty lies in the connection circuit diagram. The basic difference is that there is no filler connection on the radiator at all. The entire capacity of coolant is filled in the degassing tank. The degassing tank is designed and selected in such a way that it defines the topmost point of the entire cooling system including the radiator and the engine. Essentially if you draw a horizontal imaginary line passing somewhere in the middle of the degassing tank, all cooling system components including the topmost point of the radiator and everything else including the engine must perforce lie below this line. This is compulsory for the degassing tank to work. So, this defines the mounting location. Now, go to the circuit diagram. The degassing tank has to have an outlet connection of sufficient diameter, which is connected to the "suction side" of the water pump. Suction side is important. The first beauty is that when the engine is running, it continuously "sucks" coolant from the degassing tank, so keeping the critical water jackets pressurized with coolant. It is logical that if coolant has to enter the cooling system, air inside it must be expelled out otherwise coolant will not flow. The second beauty is that this system provides for a passive system bleed. It is a foregone conclusion that as coolant rises into the cooling system passages, any topmost point in the system must be bled (open to atmosphere). As you can’t just leave it open, it must be reconnected to the topmost point of the degassing tank. That way when coolant is being filled atmospheric air will be expelled through this orifice and through the open filler cap. The third beauty is that it is this very bleed which will provide an escape conduit for the cavitation to escape into the degassing tank where it cannot cause any harm. The fourth beauty is that the degassing tank volume is always decided in such a way that it must be filled partially. Some portion at the top of the degassing tank is the "expansion and cavitation volume"). The fifth beauty is that the filler cap although pressurized does not need two seals, as its outlet to atmosphere is natural. So the pressure cap does not become an overly critical design.
Procedure to convert the car - This procedure is indicative for vertical flow radiator fitted to a non-AC car, fitted with an alternator. For other variants, basic principles remain the same, however coolant inlet point may change. You will need 1 degassing tank. As the S1 came with it, nowadays you can easily pickup one from the scrap market where a lot of cars are broken down. Be careful to purchase the original filler and bleed pipes. These were supplied by Swastik rubber industries Khadki and are reinforced to handle cooling system pressure. The part number for the filler pipe is PAB48431 and for the bleed pipe is PAB48432. You will need 2 bleed pipes as the cut length may fall a little short. In order to increase its length, use a cut portion removed from the main fuel line of a broken down car. Do not use other pipes, if they do not withstand the pressure, they may burst on the road and lead you into problems. Purchase 2 nos. Marti Zen heater hosepipe clips, which will fit the filler pipe diameter perfectly. Use only Padmini S1 fuel line clips for the bleed pipe connections. Alternately you can purchase a brand new Indica degassing tank and adapt it but it is quite cumbersome to do it properly, as you will need perfectly fitting adapters. Remove the radiator and check for its general condition. Overhaul it if required. Then remove the filler connection from its top tank by heating it with a soldering apparatus (any radiator fellow will gladly do all this for a pittance) Take a piece of brass from a dilapidated radiator and solder it on the top tank to close it completely. Take one Solex carburetor fuel inlet connection, make a small hole in the topmost point of the engine side vertical face of the radiator top tank and inset the fuel inlet connection in it. That’s all on the radiator. Now take the degassing tank and attach it to the RH side of the dash panel so that adequate clearance is available to the steering gear drop arm to operate fully. You can use the M6*1.0 studs, which are available at this location which, were originally used to mount the mechanically controlled dynamo regulator. A simple fabricated bracket does the job quite well. As coolant capacity is around 2 liters and it must not be filled fully, load on the joints is not an issue. Just remember to keep the radiator bleed open when you will coolant and ensure that it bleeds through before connecting the pipe. Run the engine at around 1200 rpm. The water pump will suck the coolant down. Replenish it till around half capacity of the degassing tank and then fit the pressure cap. A pipe discharging to ground connects the cap outlet. Operate the car till normal operating temperature is reached and then refill coolant once again if required.
Please give me your comments.
Best regards,
Behram Dhabhar
Last edited by Technocrat : 4th July 2008 at 16:17.
Reason: Removed Size & Font Tags :)
|