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COMPACT COMPACTION COLLECTOR
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By JOHN F. MOON
A.M.I.R.T.E.
ROAD TEST: SD Pakamatic 20 Refuse Collector EVER since the horse started to disappear from the public-cleansing scene, mechanical refuse-collection vehicles have been becoming larger and more complicated. So much so, that in a large number of areas the more modern equipment has not been employable as a result of its size, and this has meant that vehicles such as side-loaders have had to be retained in service because of their compact dimensions. Lately, however, a few British manufacturers have introduced small mechanized refuse-collection designs, and the demand for such equipment has fully justified the development thereof. An outstanding example of this changing pattern is given by the SD Pakamatic 20, which has been in production for just on a year, and of which already more than 70 have been sold. Taking the SD Pakamatics generally—the range includes 50and 35-cu.-yd. models in addition to the 20-cu.-yd. version—more than 850 have been sold since the first model went into production in 1961, and an appreciable number of important local authorities have quite sizeable fleets of Pakamatics in service.
A few weeks ago I tested a Pakamatic 20 design, both as a chassis/cab carrying test, weights (to obtain basic performance figures) and as a complete vehicle, and the second series of tests made in the Luton area showed the ability of this model to get into and manceuvre in extremely confined spaces, whilst at the same time have sufficient refuse capacity to make it an economical proposition for normal household-collection duties also. Refuse was collected from the back of Luton market, where the access is down an alleyway with a minimum width of 6 ft. 6 in. at tyre height, and it was only because this is the maximum overall width of the Pakamatic 20 that the vehicle could be used at all for this particular operation: the time saved when compared with using the two conventional vehicles previously employed justified the purchase of the Pakamatic 20 in itself.
When engaged on normal house-to-house refusecollection service, with three loaders in addition to a driver, 194 dustbins (or the equivalent in terms of armfuls of o2 cardboard cartons) were emptied in 1 hr. 40 min. over distance of just under 2 miles, and the overall fug consumption rate was accurately measured as 10 m.p.1 including the fuel used during the three miles from ti depot to the collection area, the four miles from this ar to the tip, and the five miles between the tip and the dep The weight of rubbish collected was 1 ton 19 cwt. al compared with the amount of fuel used (for the cwt., of those people who thrive on statistics) this gives a ra of 1-393 tons of rubbish per gallon, or 138-5 bins per gallh on this particular collection round. The whole operati4 was completed in 2 hr. 50 min., and whilst it is agreed th larger mechanical collectors could easily equal these figur in districts where the roads are wide, the true economy the Pakamatic 20 shows up when the collection area laced with narrow streets and roads with small " fryii pan" ends.
This applies, in particular, in Midland and Northe towns, where there are many areas with houses bu extremely close to each other and with narrow, rear-acec ways. So the true value of the Pakamatic 20 lies not much in its straight fuel economy when engaged on norrr household-collection service as in its ability to thread way through narrow gaps and at the same time accoi modate 20 cu. yd. of normal refuse. Of course, there a rural areas where a Pakamatic 20 can be employed ve profitably on more normal duties with a crew of two, al in such cases also its mechanical compaction system n reduce the amount of dead mileage running to and fro the tip.
A Simple Collector
Compared with many other current types of mechanic continuous-loading refuse collectors on the market various parts of the world, the Pakamatic is remarkat simple, there being only one moving part performing t compaction, despite which the compaction-volume ratio 2-66 to 1 in that 20 Cu. yd. of normal refuse (with a dens of 2-5 cwt. per cu. yd.) can be compressed into a body ; space of 7.5 cu. yd.
The Pakamatic principle should by now be well nown to public-cleansing engineers, but briefly it onsists of a large double-acting packer plate which orms the floor of the loading hopper, forward movetent of which plate compresses the refuse in an pward and forward direction. There are shredder 3ngues immediately above the packer plate to assist breaking up large cartons and boxes and also aper sacks containing refuse. In the case of the 0-cu.-yd. model the hydraulic pressure in the packer am is 2,000 p.s.i., giving a force of 16,600 lb. at the ice of the 5-sq,-ft. packer plate, equal to a pressure f 23 p.s.i. A higher hydraulic pressure could be sed, as on the larger Pakamatics, but this is not esirable because too high a compaction pressure 'ould pack the body too tight, thereby making dislarge rather difficult.
A refuse-collection vehicle leads a hard life, articularly when the ground at the tip is rough, yet eansing engineers expect their machines to last for : least seven years. The SD TN-type chassis on hich the Pakarnatic 20 is based has been designed give a minimum life of 10 years and the manufactrees guarantee covers a three-year period----someling unique in the British vehicle industry. It is not irprising, therefore, that the TN chassis is a very 'bust assembly, designed specifically for refuseAlection duties and so well able to withstand the gours of such work.
The chassis side-members are 0-3125-in. thick, with maximum depth of 6-5 in. and 2-5-in, flanges, each which is reinforced with 0-25-in. thick plates, giving section modulus of 9-0. Chassis twisting over rough ound is a particular hazard for refuse-collection licks, especially when the body is tipped, and the TN layout is specially designed to reduce chassis and body twisting to a minimum.
There is a large outrigger bracket at each side of the main frame, immediately ahead of the rear wheels, and the hopper-actuating arms are attached to these so that they act as full-width stabilizers. Three cross-tubes brace the frame between the attachment points of the outrigger brackets, and these resist the frame twisting which is otherwise liable to occur when discharging on rough ground, and also prevent the outrigger arms bending up due to the pull on the actuating arms. Another feature designed to relieve the frame of stresses when tipping is the incorporation of the rear body pivots on the cross-tube linking the rear-spring rear hanger brackets.
The suspension of the TN has been carefully designed to suit refuse-collection work also. Because this type of vehicle spends comparatively little of its life carrying a full load, the main semi-elliptic springs have rate characteristics which give the best ride in the almost unladen condition. Further load brings the Metalastik rubber helpers into action, and these also assist in stabilizing the chassis when on rough ground. Another point about the suspension is that it has been designed to keep the height of the hopper loading rail constant at 4 ft. 6 in., this being the dimension generally most acceptable to local authorities.
Yet another chassis-design feature of particular advan o4 tage when discharging at rough tips is the location of tl engine and gearbox ahead of the front axle, where the weight acts as a balance to cope with the load behind tl rear axle. This layout also gives a roomy cab, with entran steps ahead of the front wheels and seating for thr loaders and a driver.
The standard TN chassis has a wheelbase of 8 ft., givi a Mini-car-sized turning circle of 31-5 ft. (35.0 ft. swep which is one of the Pakamatic 20's most valuable attribut There is an alternative chassis with a wheelbase of 9 ft. 5 for use with longer cabs providing seating for six bade although I should not imagine many authorities wou require a crew of this size with such a small vehicle.
The Perkins 4.236 four-cylinder; direct-injection die: engine (with Laystall Cromard liners) is standard in t TN chassis, and this has a 13-in, clutch to cope with cc tinuous stop-restart operation in place of the 11-in. clut more usually fitted to this engine for vehicle applicatioi The gearbox is the Ford four-speed synchromesh u normally used behind Ford six-cylinder engines which pi duce about 33 per cent more torque than the 4.236, whi the one-piece propeller shaft has Hardy-Spicer 1500-ser joints. Thus, the transmission line to the 6-ton-capac rear axle has plenty in hand to cope with numerous ste
id restarts on hard surfaces and continuous torque tctuations on rough tips.
Although the brakes have a diameter of only 12.4 in., the lings at front and rear are 5-in, wide, giving a total fricmal area of 480 sq. in., which is the same as on the TZ -ton-gross chassis which forms the basis of the 35-cu.-yd. ikamatic. The Girling hydraulic units are vacuumsisted, and the use of these small-diameter drums allows -in, wheels to be fitted to the basic chassis when the TN used with "Chelsea" side-loading bodies.
The Pakamatic 20's cab has an all-timber frame, and tensive use is made of moulded glass-fibre panels. The iving seat is separate, and adjustable vertically and irizontally, and alongside it there is a two-man seat, the shion of which forms the lid of a usefully large locker. pposite this seat is a separate seat for a third loader, who s with his back to the windscreen. Generally, the layout the controls is good, and although the gear•change lever rather a long way back relative to the driving seat, it quite easy to get used to this position and no awkward .etching is involved.
The first day of testing was devoted to a TN chassis-cab th a kerb weight of 2 tons 15.25 cwt., loaded to a gross ight of 8 tons 8.25 cwt. with three of us in the cab. .sic performance figures were obtained with this machine, d these are detailed in the accompanying data panel. ake tests were not, however, carried out as the vehicle d covered less than 100 miles before my test, so the akes were quite raw. The weather was bad also.
Although the fuel-consumption and acceleration figures :re not exceptionally good, with a vehicle such as this lization counts for more than fuel-usage rate, whilst the :..eleration was in actual practice quite sufficient for rrnal town use and, after ail, while collecting on houseId service, the most-used gear is bottom. The maximum !eds in the four gears were recorded as approximately
15.0, 28-5 and 46.0, showing the gearbox to have a isonable spread of ratios for this sort of work.
ill-climbing Test aradient trials were made on Bison Hill, which is 5-mile long and has an average severity of I in 10.5, non-stop ascent made in an ambient temperature of 15°C 1°F) caused the engine-coolant temperature to rise from 'C (170°F) to 80°C (I76°F), indicating more than suffint cooling capacity. This ascent was made in a total le of +5 min., and bottom gear was used for 2.25 min. h the engine running on the governor. The climbing le was not particularly fast, but was again sufficient for
s class of vehicle, and my main cause for complaint was .t slight exhaust smoking took place, smoking also being [iced with this particular vehicle on other occasions when 1 throttle was used Iecause of the condition of the brakes a fade test was t attempted, although the generous lining area suggests that fade should not be a problem. The chassis was taken to the 1-in-6-5 section of Bison Hill for stop-and-restart tests, and both facing up and down this gradient the handbrake held quite comfortably, whilst bottomand reversegear restarts were made without any difficulty. The theoretical bottom-gear grade-ability is 1 in +5.
The TN chassis was pleasant enough to drive, and the ride was not too bouncy despite the short wheelbase, the lever-type dampers which are standard at the front axle obviously helping to control the pitching. Unladen, however, the ride was decidedly better. The steering was a little heavy considering the low front-axle loading and was affected by road bumps also. I blame the type of front axle for this. Engine noise tended to be excessive, and top gear has to be regarded almost as an overdrive. The brakes felt entirely satisfactory, whilst the all-round degree of visibility was good: the driving mirrors looked small, but gave an entirely adequate rearward view.
The work done in Luton on the second day of the test was with a Pakamatic 20 that had been purchased by Luton public cleansing department earlier this year and had covered nearly 1,000 miles. Mr. John Stephen, the director of the department, very kindly allowed me facilities to watch this vehicle working and take performance figures with it, and what I saw was most impressive. This vehicle is not normally used for household collections, its regular assignments being to clear the market area and various schools and industrial premises.
The approach to the back of Luton market is through a very narrow alleyway which, at its widest point, is 8 ft. 3 in. and the waist-height width at the entrance is 7 ft. 9 in,, with kerbstones at this point only 6 ft. 6 in. apart. The regular driver apparently experiences no difficulty in getting in and out here, the only concession to the width necessary being to fold back the nearside mirror, which is spring loaded in any case.
Much of the market refuse consisted of wooden crates, and the ease with which the packer plate crushed these was quite remarkable, although one of the loaders had to be on hand to keep forcing the larger crates down in front of the packer plate to ensure that the remains were forced intoathe main body. The amount of refuse collected on this run totalled 2 tons 1 cwt., and this was discharged at the tip in 35 sec., this time including shunting the vehicle a few feet in order to shake the load clear of the body. Fully laden, the front wheels were carrying 2 tons 15-5 cwt. and the rears 4 tons 15-5 cwt., whilst unladen the distribution was 2 tons 3 cwt. and 3 tons 8 cwt. respectively.
Normal bin collection from a housing estate was carried out in the afternoon, and this made me realize that nowadays a dustman's job is almost white collar work, so little dirt was involved. Three loaders were used for this work, and the hopper was continually being cleared without difficulty by the action of the packer plate, whilst the vehicle's compact dimensions and tight turning circle reduced time wastage to a minimum when turning in narrow roads. Although not a "dustless " collector in the true sense of the word, very little dust blew about when bins were emptied into the hopper. and the noise of the engine— which was kept running at about 800 r,p.m. to power the hydraulic pump—was not sufficient to disturb occupants of adjacent houses.
The value of the rigid chassis frame and the body stabilizers became apparent when the vehicle was discharging at the tip. 1 watched several of Luton's 14 50-cu.-yd. Pakamatics working at the same tip, and in the case of these also there was hardly any relative movement between the body and the frame, no matter how rough the ground. Discharging was a simple matter, and when fully tipped there is 5 ft. 6.5 in. clearance between the ground and the bottom of the hopper, thus there is little fear of the vehicle dragging Its discharged load behind it when moving away.
The Pakamatic 20 has a list price of £3,450, and its overall usefulness makes ihk a very reasonable figure. The engineering and quality which have gone into the design are readily apparent, whilst its comparative simplicity should help to make it an easy vehicle to keep working full time for years and years.