Wednesday, 13 June 2018

Range Rover P38 second air suspension pump

2nd Air suspension (EAS) pump 

My Range Rover 38 is fitted with Arnott Gen 3 suspension air bags - these bags are considerably larger (both in length and diameter) than the standard Land Rover items, and as such, require more air to fill and extend them to their maximum height.

I think it's fair to say the standard EAS pump on a Range Rover works at the top of its operating limit, even when the system is healthy, so the fitment of these bigger bags really puts a strain on the already stretched pump.

To counteract this, I've fitted a second pump. I did consider simply removing the standard EAS pump and swopping it for a larger capacity unit, however there are space limitations, and the pump location is far from ideal.

There are issues which need to be considered when fitting a second pump, the primary one being moisture. The standard EAS system draws air in through a desiccant drier - as air is drawn in, the drier traps moisture, keeping the EAS system (especially the valve block) nice and dry.
In addition, when air is released from the system, it is passed back through the drier to atmosphere, removing built up moisture from the desiccant as it goes - the drier is only effective if this 2 way cycle is maintained.

The problem with a second pump is that if air is drawn through a different source, the drier does not contribute to the system - you have to be really careful about how air is treated as it enters or moisture may become a problem. In addition, if you use the air for other things (my system is plumbed to a tyre inflator - see separate blog) the drier may become saturated as the 2 way cyclic process is not being fully carried out.

Rather than simply adding another Dunlop pump, I've gone with a Viair unit. The standard pump is a high pressure low volume unit, whereas the Viair pump has a far better CFM flow rate - in fact the model I've gone for has almost 7 times the cubic capacity compared to the standard pump.

To add the pump, I've opted to leave the standard EAS system alone as much as possible - here's the basics


  • The 2nd pump is permanently mounted in the boot, in the spare wheel well
  • Power is supplied via a separate fused switched circuit (see separate blog) - I can choose when the pump is on or off
  • The switching of the pump is via a pressure switch (identical to the standard switch) - even if I accidentally leave it on, it should not over pressurise the system
  • The circuit is ignition controlled - I cannot accidentally drain the battery running the 2nd pump
  • The 2nd pressure switch is Tee'd into the existing valve block feed line, just adjacent to the EAS valve block
  • The feed line from the 2nd pump is direct to the tank - it does not feed directly into the EAS line(s)


The pump draws air through a filter drier mounted in the void behind the base/CD changer unit (nearside rear boot) - this seemed a reasonable inlet point - it's well out of the way of potential water and mud/dust etc. and is hidden by trim.


Note the pump on the left - the battery you can see is part of my split charge/rear winch, and does not supply the Viair pump.

The standard EAS system draws from/feeds into the air receiver at the rear of the tank. However, at the front of the tank there is another screwed plug. I removed this plug and drilled and tapped the centre 1/4 BSPT, and have used it as a second inlet point - this means the standard EAS again is un-molested.
In addition the standard system uses 6mm pipe, however I've tried to optimise the extra capacity of the Viair pump, so my 2nd feed line runs into the front of the air receiver tank via 10mm plastic hose and push-fit fittings.


New 10mm tank inlet

As a side note, for push-fit metal fittings I've found Kelm to be super reliable, and for plastic fittings, I've never been let down by John Guest fittings. I always use a blunt pencil sharpener to feather the edge of the cut pipe, and a dab a bit of Vaseline on before inserting the pipe into the fitting.

I made a simple 2 way manifold for the pressure switch, and a bracket to mount it off the cruise control assembly under the bonnet - this was the easiest and closest place for the electrical wiring - the 2 relays are under the passenger seat, with the off/on switch where the ashtray used to be.

For the 2nd pressure switch I've gone for a standard EAS unit to prevent the two systems cancelling each other out. It's important the standard pump is triggered, or the EAS ECU will throw a fault (it wont understand how the suspension can still go up but the pump has not been used) - this system triggers both pumps when the pressure is reduced, but the Viaiar is so powerful, the standard unit is only on for around 30 seconds or so - apparently that's enough to keep the EAS ECU happy.


2nd pressure switch arrangement

Although I've only recently relocated the pump to the spare wheel well, and plumbed and wired the system "properly", I've run the system jury rigged for 3 years now, and it's proved fantastic - the extra demand of the Arnott bags is never a problem, and because I use my EAS a lot, she seems to be venting often enough through the drier to keep the desiccant effective.

The EAS system remains happy, with no soft or hard faults as a result of the installation.

In the UK, everything Viair is available through Matt Savage, and the customer service support team in the USA are also pretty helpful if you need them.

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