The South Devon Railway's Routemaster

Nitrogen, An Intensifier Alternative

Since the LT Intensifier is a bespoke unit and acquiring one is virtually impossible for a one off, then for the small fleet operator or enthusiast there is an alternative, Nitrogen.
Nitrogen is the principle gas in the atmosphere so it can be considered to be "dry air" for the accumulators.  The reason LT used the intensifier was cost and simplicity; just consider how many Routemasters they ran.

You will need a cylinder of oxygen free Nitrogen from BOC (or similar) which has an initial charge of 230 bar (cost, at the time of writing, £62.00 (£47.65 for hire + the rest for the gas)), a suitable regulator (BOC Part RS600 cost £155.00+VAT ), a Schrader charging connector capable of at least 40 bar (USA Part No is a 556; EU Part No is 32284-67 Connector,3000psi, 1/8" NPTM,7.747x0.794 £35.36 inc VAT & P&P) and a 4m length of suitable ¼" hose from a specialist supplier with the relevant fittings crimped onto the ends.  Remember the pressures here are very dangerous and MUST be respected.
At the time of writing the Schrader catalogue can be found here and the 556 connector is on page 7. This document may change.

A cylinder trolley is a wise idea for moving the kit around.  They're not that expensive and are available from gas supplier.  We also keep the relevant spanners on the trolley so everything is easily to hand.

Charging the accumulator(s) is(are) very easy.  Follow the instructions in the "Brakes" page for connection etc. but instead of connecting the intensifier air line connect the Nitrogen supply hose having ensured that the Nitrogen cylinder regulator is at its lowest value (off) .  In the case of Schrader charging connector 556 turn the Tee handle clockwise to open the valve on the accumulator before opening the cylinder isolating valve. Any residual pressure will be released into the hose and the regulator output gauge will indicate this pressure.  Open the cylinder isolating valve and then gently screw in the regulator handle so the output gauge records an increasing pressure until 550psi (38bar) is reached. STOP at this point.  Allow the pressure to stabilise and then, in the case of this set up, close the Schrader valve by turning the connector Tee handle anti-clockwise.  Return the regulator to its lowest setting (off) and isolate the cylinder.  Now gently undo the Schrader charging connector to vent the hose pressure; do NOT remove from the accumulator until all surplus gas has been exhausted.  Check for leaks; refit the dust cap and then repeat process for the other accumulator.
Note that if the accumulators are severely discharged then it may be necessary to release any build up of hydraulic pressure by applying the foot brake during charging to return the surplus oil to tank so the accumulators can be fully charged with gas.


In the case of RM1872 after recharging the accumulators we ran the engine to put the flag back up and then, with the engine off and ignition on, we got 24 no engine brake applications before the flag dropped again.  The MOT requirement is NINE.

Nitrogen cylinder with regulator
The Nitrogen Cylinder with gauges attached
Hose assembly
The complete hose assembly
Regulator detail
Schrader valve
Schrader Charging Connector 556
Charging the rear accumullator
System in use charging rear accumulator

For more information contact the South Devon Railway on 0843 357 1420 or by

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© South Devon Railway Trust (RM1872) 2005-12

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