Pressure Regulator - Stripdown and Rebuild

As far back as 2015 I'd given the pressure regulator from my car a refresh, though I hadn't really given it a good going over. The chamber on the side that the HP pump pipe connects-to was made of plastic, so I removed it before using a wire wheel to de-rust the metal body.  

From my DS: Plastic Side Chamber - 19 July 2015

I put the two parts back together and gave it a spray of paint - that was it really........

......Only that plastic side chamber had always niggled me. I hadn't expected it to be plastic.  I was worried it might snap at the hose union. All my research showed that a DS pressure regulator had a metal side chamber. If it wasn't intended for a DS, then was it set up for the right pressure inside? 

At the 2017 Citromobile rally in Holland I found an all metal regulator - still fitted to a DS mounting bracket -  for a few Euros so snapped it up. 

I decided to strip and rebuild it for the learning. Then I could decide whether to use it on my restoration or not. More recent research turned up a photo of a regulator with a plastic body - being sold as a replacement for a Citroen BX. If that was so, then I definitely wanted to use this new pressure regulator.

Spot The Difference

Instructions for stripping and rebuilding the pressure regulator can be found in Operation DX. 391-6 in manual 518 although, being the earlier manual, it deals with the earlier aluminium bodied regulators which have a distinctive screw cap. If your car has one of these, then all advice is to seek to replace it with a later steel-bodied one. You really need to seek out a copy of volume 3 of French language manual 583 for the more up to date Operation D. 391-6. You can find the link to it on another tab on the 'workshop manual' tab of this blog.

There is also a very handy two part 'DSSMPassion' video on Youtube. Here's the link to the first part.

Pressure Regulator - strip down video part 1

I bought a rebuild kit from Citroen Classics. this consists of a few rubber 'O' rings and two new ball bearings. The kit from Der Franzose is similar but includes two new springs. That might be an important consideration, as it's the springs that do all the work and get 'tired'.

Removing the side chamber revealed a load of sludge.

Slide Valve and Sludge - 18 February 2018

There was also an 'O' ring to fish out.....

The shiny bit in the middle is the domed end of a slide valve. It has a circlip on one end that stops it moving completely through the passage. I removed the valve with a gentle squirt of compressed air down one of the hydraulic pipe shafts.

Slide valve

I removed the large bolt for depressurising the accumulator. Hidden behind this is a ball bearing. In the end that the accumulator sphere screws to, there is a small 'U' shaped bracket held in place with a bolt.

Removing the 'U' bracket revealed another ball bearing.The dull grey circle in the middle is the flat end of the other slide valve. This was removed with a squirt of compressed air

The 'DSSM' strip down video makes reference (at the 2:09 mark) to the workshop manual technique for removing the end cap. You won't find it in manual 814. (814 doesn't include any information on stripping the pressure regulator). Unusually won't find it in manual 518 either! You need to search out a copy of volume 3 of French language manual 583 and look up the later pages of Operation D.391-6. You can find 583 by following the link to the "Tony Jackson" dropbox site. Details of this are in the 'workshop manual' tab of this blog.

The end cap covers a powerful spring and is held in place with a circlip that locks into a recessed groove. Because of the recess, this is near-impossible to winkle out once it's been fitted and painted over..... The technique is to drill a small hole through the side of the body  in line with the recessed channel that the circlip sits in, and then to insert a pin to compress the end of the circlip. This then gives you enough purchase to lever it out.

By looking at the circlip, I marked my drill point to be in the gap of the circlip. I didn't want to drill through the circlip! That's true, but as I wanted to drill on the back, unseen side of the body I actually rotated the circip with a screwdriver blade so that the gap would be where I wanted it to be. The manual says  to use a 2.5mm diameter drill to drill a 'keyhole' 4mm in from the edge - inline with the groove the circlip sits in.

Drilling a 'Keyhole' to release the Cap Circlip.

With the hole drilled, I rotated the circlip so one open end of the circlip was just over the hole. With one of the long mounting bolts for the pressure regulator in the end cap (a long bolt meant I had working room between the jaws of the vice), I used a vice to compress the end cap just enough to take the pressure off the circlip. 

Pushing the flat end a twist drill through the hole I'd drilled, I was able to press down on the circlip edge to free it from it's recess, and then get a small screwdriver blade underneath it. It was soon out.

Cap and Spring Compressed. Circlip Removed - 18 February 2018

I slowly opened up the vice, being careful to not let anything fall out of the end of the regulator. I laid out the parts so I could see what i was dealing with. The ginger nut was not part of the assembly. 

With the spring removed from the end cap, I discovered a number of thin shims. 

Closer inspection revealed more shims in the end of the side cover I had removed earlier. All had been difficult to see as they were covered in black sludge.

I assume that it is the number of shims that are used to set the operating pressure(s) of the regulator?

Since my kit didn't include replacement springs, I pulled apart my other regulator (why not!) and compared spring lengths. They seemed to be consistent - meaning that either both sets were worn and compressed to the same degree - or neither were.

All parts were carefully cleaned without abrasives. The body was washed in Jizer and rinsed, and all the passage ways were blown out with compressed air.

The regulator I was rebuilding still had some Citroen codes and maker marks on it - so was the original colour. I was keen to see how the paint colour I used back in 2015 compared to the colour of an original. It was close but not a perfect match. I wasn't fussed as the colour of the 'original' was different to other 'original' parts I had too!

Comparing Paint Colours - original and my first respray

I cleaned the body with paint stripper and on a wire wheel before treating it with phosphoric acid. I was careful that none went anywhere near the slide valve bores. I gave the body an initial paint up before re-assembly

Here's the rebuild video from "DSSMPassion":

Pressure regulator - rebuild video

The seal in the cap was lubricated with LHM and replaced as was the seal on the de-pressurising bolt. I masked the threads of this bolt with tape to enable me to slip the 'O' ring over them without tearing it.

Replacing the seals was the secondary purpose for this strip down. Other than a flat accumulator sphere, the main reasons for a poorly performing (very low cycle time between 'clicks') pressure regulator is wear between the slide valves and their shafts. My strip down would not tackle this but would, at least, enable me to clean out any sludge and to make sure all parts were free to operate as intended. 

The ball bearing in the body was replaced, as was the one behind the de-pressurising bolt. All the parts were re-assembled and lubricated with LHM. I used a vice to compress the cap into the body - being careful not to pinch the sealing 'O' ring. The circlip was replaced and the vice opened up.

All apertures were blocked once more, before I gave it a final coat or two of paint.

Just for the hell of it, I tried a different colour on my first regulator (left hand one in the photo below)  - but it looked wrong.

I stuck with the original colour I'd chosen for my hydraulic parts - BS 226 - on the right in the photo above.

With the mounting bolts zinc-plated, it's all ready for the refit!