Steam Brake Air Tested

In June 2012, I last wrote about Sentinel 7109's steam brake cylinder. Time passes and I've learnt that restoration is not a rapid activity!

The brake cylinder was reinstalled on Monday 7th December 2015 and here it is in place bolted to the left hand frame member to the rear of the boiler. (Bearing in mind that I can only just lift the cylinder on my own, getting it into place under here was not a straight forward exercise and required a selection of trolleys, levers, bits of railway sleeper and a lot of ingenuity to get it home!).

Brake Off

Spot the difference!

Brake On

To see it in action, here's another of my little video clips (Also on YouTube).

Sounds like heavy breathing!

The testing involved connecting a compressed air supply to the Driver's Brake Valve (DBV) inlet. Movement in the video was controlled using the DBV itself as would be normal practice with a steam supply.

DBV Top Left

The brakes still need to be adjusted but that can't happen until the front drive chains are in place and the axles located for the correct chain tension.

Checking back over the 'blog, I've not been able to find anything on the Driver's Brake Valve itself. I've had the photos since December 2012 but they slipped through the net.

The Driver's Brake Valve has an operating shaft and three connections to it - the steam supply inlet from the boiler; the outlet to the brake cylinder and a drain to atmosphere to release the pressure on the cylinder piston to let the brake off after application.

DBV connections

DBV Operating shaft

The operating shaft is extended across the rear of the cab to allow the brake to be operated from either side.

Dual Controls 1927 Style!

I took the following photo just after taking co-ownership of 7109 in 2010. A few bits & pieces had been removed and examined ('played with'). There was a long journey ahead!

DBV in October 2010

For completeness, here's the Sentinel factory drawing of the DBV. It is a general drawing showing that it could be operated from either end although 7109 did not use it that way.

Sentinel DBV Sectional Drawing

Other locos mounted the DBV in the centre rear of the boiler with handles either side.

DBV in Sentinel 9599 (William Mk1)

Vacuum Braking (13) Implementation (7)

Sunday May 31st 2015 has been mainly about the vacuum braking pipework but not entirely.

In my last article, I'd begun to assemble the vacuum ejector pipework. Now I've pretty well completed it as shown below.

Steam supply linked to the Ejector

The main work was either side of the blue pressure reducing valve (PRV).

PRV, condensate drain valve and unions at either end

Both upright ends had to be parallel in order to mate with the union counter parts. (If I've not said before, unions allow the pipework to be taken apart and also enable rotation).

In the above photo, there are unions at each end of the pipe but, in the first photo, the upright larger diameter pipe also has unions allowing it to rotate. In this way, the distance between the PRV and ejector has been made non-critical and hence much easier to assemble.

The next task was to add some support for the vacuum hoses. Previously the 'Swan necks' on the buffer beams had left only a short length of pipe to attach the hose. I'd felt that some extra length was needed in case the hose could lever itself off.

Lengthened 'Swan neck'

The extension was made from a straight pipe coupling and spare male threaded pipe. The threads were sealed with Heldite.

Comparison with usual hose attachment

The extension is still a little short compared to a normal hose fixing. However, if there is a tendency for hoses to come adrift, the extension can be extended further to fix the problem!

Some time ago, I decided that I wanted to take the steam supply for the whistle and pressure gauge from the safety valve assembly instead of the two outlets at the ends of the four-way manifold which feeds the superheater. It saves one expensive isolating valve and make the valve actually reachable by hand!

I thus had to block the manifold outlets. I used a heavy duty steel cap for one end and a coupling and plug for the other (I had the cap already and I couldn't get another off the shelf).

Since these items were round, I was advised that a Stillson wrench was the best way to tighten them despite the likelihood of some surface damage in the process.

Screwing it up!

To ensure a good seal, I made a pair of thick annealed copper washers and applied a liberal amount of Steamseal to make sure.

The cap fits

The Plug fits!

Now to make a hole in the roof for the ejector exhaust.

Vacuum Braking (12) Implementation (6)

My previous article on the braking pipework finished with a view of the beginnings of work in the cab. To say this involved some unsightly contortionist-like activities is an understatement because the space in which to fit this pipework is bijou to put it mildly. After a day of this, I need a day away to recover!

It also doesn't make it easy to take good photos. I hope the gist is clear from the following ones.

The first is the driver's eye view looking forward.

Avoiding the window and other pipework

I had originally planned to have the train brake handle below the cab's opening on the right. However, there are other bits and pieces reserving space on the side-panel such as the lever for remotely operating the exhaust condensate valve. It would also have meant the pipework passing under the shelf supporting the boiler feed pump where there are other pipes to be installed.

So I concluded that the best route for the pipe was around the top of the circular window aperture with the brake lever much higher up. Top right in the photo are the yellow-coloured silencer/air filter where air is let in to apply the brakes. Then there is the blue-handled brake valve lever itself with the vacuum relief valve just beyond it pointing up at an angle. There is a connection for the vacuum gauge right at the front.

It was not an easy job fitting the pipe around the window particularly the elbow at the top left. The pipes won't bend or give so they have to be exactly the right dimensions to go together! (I got it right on about the third attempt!).

The next photo is looking down to where the vacuum pipe passes through the cab floor (see the last three photos of this link).

Connections to the train pipe,check valve and Ejector

I've put a right angle in between the check valve and the ejector to shorten the length of the steam feed pipe. Hopefully this will reduce the length and weight of suspended pipework.

Ejector's steam feed

The ejector's steam feed is taken from below the left hand safety valve manifold branch (left foreground). It passes through the blue pressure reducing valve to the ejector via a cross (+) fitting which will allow for connecting a condensate drain valve and an ejector-feed pressure gauge. (The pressure reducing valve needs to be set to feed the ejector at its optimum pressure - 60 psi).

Next I have to assemble the safety valve manifold with steam seal and complete the ejector connections. Some extra Stauff clamps are also needed to support the vacuum pipe. Then there is the ejector exhaust pipe which will require a hole in the roof. Hmm, I'd better get that in the right place!

Vacuum Braking (11) Implementation (5)

Following on from Vacuum Braking (10), it really is true that the whole pipe structure can be dismantled and removed and here it is laid out on Midsomer Norton station's down platform.

Front to rear vacuum pipework

The next job was to replace it all beneath the footplate and frames, then to complete the Stauff clamp fixings and tighten it all up.

The fixings presented another opportunity for the sky drill under the water tank.

Suspended on rails between the rails

The holes were tapped for M6 mounting screws (or, in this case, twice over as the tap tool broke and had to be left buried deep in the water tank metal work. It's covered by the clamp now so nobody will ever know!).

Clamp and hidden holes

Forward-most mounting clamp

Earlier I'd had trouble aligning the hole through the cab floor with the pipework's 'T' junction below. Having started to tighten up the clamps, the situation was beginning to get worse. Previously I'd enlarged the hole to a figure '8' shape; now the hole still did not seem to be long enough but this time I'd run out of space in the cab due to the sanding gear cross-shaft.

My only option was to put a kink in the pipe to realign it.

Joyce's Kink!

Now things were starting to behave themselves and I was able to fix another Stauff clamp and bracket in place to support the pipework from above.

Clamp, bracket and sanding gear cross-shaft (red bar) near the cab front

Finally a quick mock-up of the ejector (aka. jet pump, 'little sucker'), non-return valve and 'T' for the brake operating handle - all connected to the completed pipework below (and Joyce's hidden kink!).

Ejector and non-return valve

Now I'll be able to spend more time in the cab instead of underneath, flat on my back. Having said that, there's a lot more space below. Lonnie Donegan summed it up a few years ago: "There's not mushroom inside"!

Nut & Bolt - Big Time! (2)

A few months ago, I described the manufacture of a new nut and bolt to operate Sentinel 7109's handbrake. Today I fitted it into place.

Linkage from nut to crank(1)

Linkage from nut to crank(2)

Some large split pins are still needed to complete the job. The largest I had are 1/4" diameter. 3/8" are needed. These things are big!

Optimism!

The brakes will have to be adjusted after the drive chains have been fitted but they do at least operate from the handle. The roller bearing under the handle seems to work satisfactorily.

Nut & Bolt - Big Time!

Years ago, my mother recounted the story of her first driving lesson in which, once she had got the car moving, her main concern was how on earth to stop it!

Health and safety aside, the principle has stood the test of time. Sentinel 7109's original handbrake screw thread was clearly beyond use when it first arrived at Midsomer Norton. I never took a photo of it but the square shaped 'Acme' thread bore a strong resemblance to the 60 degree angles of a metric thread profile! As the last resort for stopping, it did not provide much in the way of confidence!

The way the handbrake works is quite simple. It's a big vertical bolt with a handle and a nut that's linked to a crank. When the handle is turned, it pulls on the crank which pulls on the brake. (There's some more about it here: Steam Brake Cylinder).

Handbrake Nut and Linkage (below cab floor)

Handbrake Handle (above cab floor)

Best efforts were tried to repair the damaged thread by machining it away and welding new metal in place to allow a new thread to be cut.

It worked initially as in the video below (Also on YouTube).

However, after a while, the cutting tool decided it wanted to dig a little deeper and pulled off some of the metal causing a complete write-off of the original shaft.

Mendip Steam Restorations were tasked with the job and completed both the finishing of a new nut (with posh phosphor bronze 'Top-Hat' insert) and a new handle shaft.

New Handbrake Shaft and Nut

The original handle assembly has been attached to the top of the new shaft. I wasn't sure about a plain thrust bearing and decided that, for minimal cost, a roller thrust bearing could be used as shown below. Whether it will prove strong enough in practice, I don't know but at least there is the fall-back to the original construction.

Roller Thrust bearing below the handle

New nut & insert from below

New nut & insert from above

So, with any luck, we'll now be able to stop 7109 after we've made it go!

One feature which I do intend to add is a shield of some sort to prevent grit getting into the thread; hopefully this will prevent the damage that happened to the old one.

Vacuum Braking (6) Testing (1)

I have to admit to being mildly excited! I'd previously been unable to include an article on Sentinel 7109's Jet Pump (Vacuum Exhauster) device itself and only realised today when I'd completed a highly sophisticated (i.e. garage based!) compressed air test of it.

So here is the little sucker:

Penberthy GL-1 Jet Pump

It's not very big as can be seen from the picture (hopefully it will be big enough!). Steam (or air) enters from the right and exits on the left. It draws a vacuum through the sideways port.

For quite some time, I've had to be satisfied with the calculations I'd done in selecting this particular Jet Pump; however, it's not a technology I've been previously familiar with and have also been at variance from others who have fitted vacuum exhausters to Sentinels before. So my R&D has not been without some risk as to its success.

My first attempt at testing the jet pump was to connect it to an air compressor. However, this produced a poor result which I put down to the narrow bore of the air feed pipe being less than the bore of the jet pump itself. Thus it was never going to be able to feed sufficient air at the required pressure (around 60 psi).

By a stroke of luck, I found a scrap air cylinder at Midsomer Norton Station that had a 1/2" bore outlet and a valve. I considered that if I could pump this up with the compressor, I could then use it to feed the jet pump from its 1/2" bore outlet, at least for a short time anyway.

So here's the test rig in all its sophistication:

Jet Pump Test Rig

The air cylinder is on the left with the compressed air inlet at the top via the orange pipe fitting. There is also a non-return valve on the inlet. The valve controlled outlet is by the black air pressure gauge. The jet pump is above with an Ex-BR vacuum gauge on its suction port. The jet pump outlet is skywards.

This time I was much more successful (which led to my excitement that what I'd calculated actually worked!).

Vacuum gauge showing 21" Hg with about 66 psi air pressure
(It's easier to read on its side!)

I'm not concerned at the 66 rather than 60 psi. Neither gauge has been calibrated so the figures cannot be relied upon absolutely; however, I'm satisfied they are good enough to show the principle.

Here it is in video form: (also on YouTube).

Jet Pump Test

Some years ago, I visited the USA when printed 'T' shirts were becoming popular. I bought one with the message: "Engineer - Individual who turns abstractions into malfunctions". Hopefully not always!

Vacuum Braking (4) Design (3)

Having settled on the GL-1 Jet Pump ejector running at 60 psi in Vacuum Braking (3) Design (2), here are the next three challenges:

1. How to connect the Ejector's American NPT threads to UK BSP threads?

2. Selecting a Pressure Reducing Valve to take the 275 psi boiler pressure down to 60 psi for the ejector.

3. Selecting a Vacuum Relief Valve for making sure that the Jet Pump does not draw more than 21" Hg of vacuum.


1. The GL-1 Jet Pump Ejector has a 3/4" steam inlet pipe thread and 1" exhaust and suction pipe threads. The trouble is that the American NPT and British BSP threads are not generally compatible and Sentinel 7109 uses BSP threads.

There are two challenges here: the pipe threads themselves and the need to be able to assemble and disassemble the ejector from the rest of the pipework. Initially, I'd started to look for simple female NPT to female BSP pipe couplings. However, it occurred to me that, if I could find a pipe fitting supplier with both NPT and BSP threaded unions, the thread linking the union halves might be the same. Thus it would be possible to create a union with NPT thread at one end and BSP at the other.

Mixed NPT-BSP Union halves

After a lot of internet searching, I eventually found Nero Pipeline Connections Ltd who seemed to have what I was looking for in stainless steel. I rang Nero and a very helpful Daryl offered to go and actually try a NPT and BSP union together. He rang back proclaiming a success with a proviso that I might have to do a little fitting to ensure a good seal between the dissimilar union halves. This was the sort of service I needed and have been able to obtain what I needed as in the photo above. Having tried the dissimilar halves together, there does not seem to be any need to persuade them to fit with each other.

2. The Pressure Reducing Valve not only has to drop the boiler pressure from 275 to 60 psi to suit the ejector but it also has to be able to let enough steam through for the ejector to do its job (and possibly a bigger ejector if ever needed).

I'd been guided towards Spirax Sarco as a suitable supplier partly because Gervase was already using one successfully but also because another Sentinel had a different type which had the persistent habit of blowing a continuous Raspberry! This was not a particularly attractive feature and one which was worth avoiding if possible (I'll diplomatically not say which Sentinel has this feature!).

Spirax Sarco BRV2S rated at 276 psi and 212 Deg C.
with Orange hat.

The beast is in the photo above. It arrived very quickly from BSS in Gloucester, UK.
Two optional features had to be chosen:
(1) To ensure sufficient steam flow was possible, I chose a 1/2" type easily capable of supporting a GL-1 ejector and even a much bigger GL-2 if found to be needed later.
(2) To be able to set the 60 psi outlet pressure, I chose an 'orange' rated spring allowing a range from 3.5 to 8.6 bar (60 psi = 4.1 bar).

The full specification of the BRV2S can be found here.

3. The Vacuum Relief Valve has to let air into the vacuum pipework when the 21" Hg level is reached. It also has to be able to let more air in than the ejector can pump out so there is a size factor too.

It took me a long time to find a supplier of a suitable device. Eventually, I found Flowstar of Kingston upon Hull, UK, who distribute products made in Hamburg, Germany, by Niezgodka GmbH. The Type 91, size 1 with a Viton seal and 3/4" male thread fitting is the chosen one.
The Niezgodka VRV data sheet has most of the detail while an additional data sheet covers the discharge capacity (2nd column under '18'). Note: 1 cu metre = 35.3 cu feet).
The size 1 type is good for 50 cu metres/hour = 29.6 cu feet/minute. (I enquired about the empty cells in the discharge capacity table and, for the size 1, 50 cu metres/hour also applies at greater vacuum levels than -0.6 bar). 29.6 cu feet/minute is plenty to overcome the suction possible from a GL-1 ejector or a GL-2 should it ever be necessary. So at least I won't have to replace all the parts should I find I need a larger ejector after all!

Niezgodka Type 91, size 1

Note: the Penberthy Technical Data Manual (page 9) shows a graph which indicates that a GL-1.5 ejector running on 60 psi is capable of 13.5 cu feet/minute at a suction pressure of 21" Hg gauge (= 9" Hg Abs.). Therefore it is safe to assume that a GL-1's capacity will be less than 13.5 because it is smaller. A GL-2 is not twice the size of a GL-1.5 so the 29.6 cu feet/minute of the VRV will be more than a GL-2 can remove.

Next, I'll look at the boiler's isolation valve, the reason why a curvaceous syphon pipe is used with a steam pressure gauge and possibly at the driver's brake valve.

Vacuum Braking (3) Design (2)

Having laid down the requirements and played with some design ideas, now it's time to start making some decisions and begin the shopping.

The decision from which follows all the other design choices is the size and capacity of the Vacuum Ejector (Jet Pump).

I've decided to use a bronze Penberthy GL-1 Jet Pump operating at 60 psi and which has a vacuum pipe of 1" nominal inside diameter. (see pages 8, 9 of the link)

This is why:
Extracted from the Penberthy Jet Pump Technical Data manual, this is the sequence of activities to determine the best item for the job.

Instructions

So step 1 converts our requirement for four Mk1 carriages (16 cu ft/30 secs) into minutes/100 cu ft/min. which equates to 3 minutes/100 cu ft.

For steps 2 & 3, have a look at the table below (also extracted from the Penberthy Jet Pump Technical Data manual (click it to make it readable)):

Jet Pump Selection Chart

This next table of conversions is also needed in step 4 to determine the steam consumption (right hand column above) for Jet Pumps other than a 1.5" size.

Conversion of table figures for non-1.5" Jet Pumps

In the first table, I've highlighted the GL-1 column and the 60 psi 10" Hg Abs. row. (From the table, the GL jet pumps seem to be most efficient at around 60 psi. 10" Hg Abs. is equivalent to 20" Hg gauge which is the nearest figure to the 21" Hg gauge vacuum level to be achieved).
Two columns to the right of my highlight, is a figure of 3.7 for a GL-1.25 jet pump. Although the figure is fairly close to the 3 minutes/100 cu ft required, the GL-1.25 uses 2.9% of the boiler capacity (See Vacuum Braking (2) Design (1)). Whilst 2.9% is OK (135 lbs/hour), a GL-1 uses only 76 lbs/hour or 1.6% of boiler capacity. With these figures, it's worth having a look again at the original requirements.

(The lbs/hour figures come from the right hand column of the first table multiplied by the capacity factor for the size of jet pump in the second table. The first table is normalised for a 1.5" jet pump but converted for other sizes by the capacity factor to avoid having to produce a separate table for each jet pump size, e.g. a GL-1.5 at 60 psi working to give 10" Hg abs. vacuum uses 221 lbs/hour. A smaller GL-1 uses 0.344 x 221 = 76 lbs/hour - only 1.6% of the boiler's 4600 lbs/hour capacity).

Requirement 1 was for four Mk1 carriages, i.e. 16 cu ft of evacuation space in 30 seconds. In fact, 16 cu ft only needs to be evacuated fully when the system has been full of air. Once evacuated and the brakes applied, because the carriage vacuum cylinders are still partly evacuated, the full 16 cu ft volume does not need to be evacuated. Hence the requirement can be relaxed to some extent.

Requirement 1 assumed four Mk1 carriages. At Midsomer Norton, it is very unlikely that as many as four would be involved and two carriages or occasionally three would be nearer the mark.

Thus if two carriages are involved, a smaller GL-1 should be able to evacuate 8 cu ft in 30 seconds and reduce the steam consumption accordingly.

Arguably this is cheating; however, without an original requirement figure, it is very difficult to know what to aim for. Having gone round the calculation loop once, the implications of the requirement have now become apparent and show that there is a good pragmatic case for using a smaller Ejector - particularly if it is being run continuously.

Compared with the Penberthy No. 3 size water lifting ejector having a 1" suction pipe size, the GL-1 has the same suction pipe size but is specially designed for sucking air and not water. So, intuitively, the GL-1 is a similar size to the No. 3 type used on other Sentinels but should perform more efficiently.

Recalculating the figures for two Mk1 carriages with a GL-1 Jet Pump gives a time of around 0.5 minutes to evacuate two carriages whilst using 7.6 gallons of water per hour.

Well! That's the theory anyway.

These Penberthy Jet Pumps are imported by Jenex Ltd of Great Yarmouth, UK. I'm very grateful to Mark Collins of Jenex for helping me to order the right item.

Vacuum Braking (2) Design (1)

In Vacuum Braking (1) Requirements I set out the way I was thinking about approaching Sentinel 7109's vacuum braking system. Here I'll develop my initial design ideas but show that a discussion with a more experienced engineer can reduce time, money and complexity. (Many thanks to Steve Roberts, Engineer, at the Middleton Railway in Leeds).

Firstly, on looking into the symbols needed to draw a system such as this, I found that there was some diversity in websites depicting what I hoped would be a standard. Anyway, these are what I've settled on for subsequent diagrams. (Click on the diagrams to enlarge them).

Diagram Symbols' Definition

I had two ideas which I felt would satisfy requirements 1-4 in Vacuum Braking (1) Requirements. The first is fairly simple, the second more complicated and to get over a potential problem with the first.

Single large ejector

From left to right: the boiler at up to 275 psi feeds a globe valve used to isolate the system when not in use. This feeds a pressure reducing valve to take the pressure down to a level better suited to a vacuum ejector. A pressure gauge is included at this point to measure the setting of the reducing valve.

I've then shown a press-to-open whistle valve to allow steam to the ejector. The idea is that, by using a single large ejector, it can be switched-in and create a vacuum quickly only when required. Thus, a little leakage in vacuum can be overcome by a quick 'blip' on the whistle valve. (More to follow).

The ejector sends its exhaust to atmosphere - preferably via the ash-pan to help reduce clinker formation although it would be more spectacular to send it up through the cab roof!

The ejector's suction port is connected to a swing-flap check valve to maintain the vacuum when the ejector is switched off. Otherwise air could enter the system via the ejector's exhaust port.

Next comes a DMU type of brake valve. This enables the driver to connect the train pipe to the ejector to release the brakes ('Running'), to connect the train pipe to atmosphere to apply the brakes ('On') or to seal the train pipe to hold the braking vacuum at the level set ('Lap').
The brake valve feeds the train pipe where there is a limit valve to ensure that no more than 21" Hg vacuum is generated.
Finally, there is a vacuum gauge to let the driver know what his brakes are doing. They are off above about 18" Hg.

The above seems OK assuming that there is only a small amount of leakage in the train pipe. If the leakage is greater then a second smaller ejector can be added to operate continuously in parallel with the large ejector.

Additional small ejector

The small ejector follows a globe valve used to isolate or reduce the steam supply to the ejector. Another swing-flap check valve follows to enable the ejectors to operate independently.

Given ejectors of suitable capacity, the above possibilities allow the four requirements in Vacuum Braking (1) Requirements to be satisfied. 21" Hg vacuum can be produced in the time required; leakage can be overcome by occasionally 'blipping' the whistle valve; the pressure reducing valve insulates the ejector from lowered boiler pressure and the DMU valve includes the driver's brake valve settings.

All looks good until some better informed experience is added.

At the Middleton Railway, I was shown a vacuum equipped diesel shunter in operation. As a light engine, its vacuum hoses were linked back to 'dummies' to seal them when not in use. With the engine running and the vacuum pulled to 21" Hg, on stopping the engine, the vacuum level dropped to brake-on levels within about 10 seconds - and this was just the engine with no train attached!

The impact of this situation would be that, with the systems above using a whistle valve, the driver would be forever distracted by having to monitor the vacuum gauge and be 'blipping' the brake valve. I doubt if that would be popular with drivers!

The 'Lap' setting of the brake valve would really not be of any use at all. (With air braked systems, 'Lap' works better because leaks are easier to detect and the sealing is of a better, more modern type).

I was also shown a small 0-6-0 steam loco with a single Penberthy No 3 ejector which is operated continuously. To apply the train brakes, air is let into the train pipe even though the ejector is doing its best to suck the air out at the same time! The No. 3 ejector is also satisfactory at pulling the brakes off in a reasonable time on its own (with the brake valve closed, of course!).

Penberthy No 3 Ejector and reducing valve with blue cap

Steam enters via the reducing valve on the right, then through the ejector which exhausts to the ash pan on the left (to dampen the ash). The vacuum train pipe is off the side of the ejector via the elbow pipe joint and to the right.

Vacuum pipe and steam supply

This system is shown in the following diagram (with an added steam pressure gauge).

Middleton Railway influenced Vacuum System

My concern with this simpler idea is the continuous use of steam when in operation. Instinctively, it seems wasteful; however, it may not be the case.

A 1.25" Tyco Penberthy GL type ejector operating at 60 psi uses 135 lbs/hour of steam. Sentinel 7109's boiler is capable of 4600 lbs/hour so the ejector will be using 2.9% of the boiler's maximum output - Not a lot! (Click here for reference information to these figures).

But does this still satisfy the original four requirements?

1. and 2. will be OK given the right choice of ejector.

3. will be unchanged and is a function of the pressure reducing valve.

4. can be dispensed with now that it is clear that considerably more leakage is involved than was originally envisaged. 'Lap' won't hold the vacuum level except with exceptionally well maintained rolling stock - an unlikely luxury to have!

So it looks as if things can be done more simply - time to do some more thinking!