Following Part 2 of Eric Lembrick’s article on the SU Pressure Pump Type “L”, published in the August 2011 issue of TTT2, I have received a number of enquiries about fitting a transil. It seems that what has given rise to these enquiries is the following advice given in para 4.12 of the article:
“Finally refit the contact blade and a Transil to protect the points”.
Why fit a transil? The points on your SU fuel pump are at the mercy of the high voltage (up to several hundred volts) that is generated each time they open, causing them to arc. The basic explanation for such a high voltage (bearing in mind that your battery is only 12 volts!) is that it is an effect that happens each time a current through a coil is interrupted.
To negate this high voltage (i.e to limit voltage transients) the transil pictured below comes with a rated voltage. Below the rated voltage there is no connection between the two terminals, but above the rated voltage the terminals are connected together (dead short). Consequently, when the points break the high voltage which is generated across them is shorted out by the transil, so saving their burning and pitting.
Fitting the transil Fitting is simplicity itself. The transil is supplied with ready made solder tag connections. All that is required to fit it is a screwdriver.
Note: Some T-Types will have been fitted in the past with a diode across the coil. Whilst this has proved to be an effective solution to reducing the voltage across the points it needs to be borne in mind that once a diode is fitted the pump becomes polarity sensitive. If a diode is fitted incorrectly, or, if fitted to a car of the wrong polarity, a pump fitted with a diode will fail instantly, causing the associated wiring to overheat or even catch fire. (The night after typing this I learnt from a TTT 2 ‘hard’ copy subscriber at our local ‘noggin and natter’ that he actually experienced this with his J2.
The advantage of a transil is that it is completely non-sensitive to battery polarity. Hence a transil can be fitted either way around and a transil pump can be fitted to any car. It can also be left undisturbed if the polarity of the car’s battery is changed at a later date.
Transil kits, complete with fitting instructions are obtainable on a non-profit making basis from John James, 85 Bath Road, Keynsham BRISTOL BS31 1SR, UK. Cost, including postage is £3.50 (UK), and £4.00 outside of the UK. Payment by PayPal is acceptable.
If paying by PayPal please e-mail me at jj(at)octagon.fsbusiness.co.uk (substitute @ for at) and I will send you a PayPal invoice.
Your transil kit will be sent inside a normal correspondence envelope and when you open the envelope you will find the transil kit and fitting instructions inside.