This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
All gas-meters bear a government stamp, and at times the stamp of the gas company, whether it be public or private. The government stamp, affixed after testing and payment of the fee according to the size, is a guarantee of honesty (for the time being), but such guarantee is little regarded by gas companies; some curious instances might easily be given to show that these meters soon have to be removed on receipt of notice. Gas companies favour a particular class and kind of meter, and it generally happens that only those meters likely to develop a "galloping consumption" are supplied by them. Meters that do not show a gradual increase of consumption, or that do not at least register the full amount of gas consumed, are those that are soon condemned, the nominal fault being either "not registering correctly", or "escape at index", "index-glass broken", "seal broken", or "requires testing", although any of these faults may exist in favoured kinds for years, if the consumer makes no complaint.
By Henry Clay.
Meters are either "wet" or "dry", the former being the favourites; but there are great differences in wet meters, some costing little more than half the price of others. Some have cast-iron cases, the more costly having tinned-iron cases. There are some slight differences in regard to the formation of the drum and overflow arrangements, and one meter is known as the "unvarying water-line", which seems to condemn all other kinds as unreliable, and consumers are naturally led to think that such a meter is about the best of its kind for them, whereas the facts are all the other way, for it errs always on the side of the gas company and against the consumer after it has been in use some time. The dry meters register more correctly, but, if the pressure in the street-mains is increased, they may pass a little more than indicated. At times they stop registering altogether, but continue to supply gas, notwithstanding the index-pointers being fixed.
In wet meters the quantity of gas is measured in the drum, which is suspended on an axle in the water, as shown in Fig. 640, and the revolutions of the drum are transmitted from the axle to the index by toothed gearing according to the capacity of the drum. Wet meters require to be fixed perfectly level on account of the revolving drum, spindle, water-level, and float, although at times they have to be packed owing to the drum being slightly wrong. The drums of wet meters are made of pure sheet tin (white metal). As the water falls the drum revolves more and more slowly, until at length the quantity passed is not sufficient to supply the demand, when all the lights will begin to jump, and, unless the meter is attended to, the gas will stop altogether. This is owing to the float c gradually sinking, until at last the valve seats itself at d, and stone the supply of gas from passing through the meter. It will be seen from this that the wet meter is constructed to stop the supply when the water is low, or, in other words, as soon as it begins to supply more gas than is registered.
Fig. 640 - 8ectional Elevations of Wet Gas- meter.
A. Inlet; a, outlet; c, float; D, valve and seat; I, water level; F, supply pipe to drum; G, drainer boi:
H, pinion and wheel operating the dial.
In dry meters (Fig. 641) the quantity of gas passing through is measured in the bellows, which open and close alternately. As the gas enters the bellows on one side of the partitions, the bellows on the other side are closed, and the measured quantity of gas forced out of them and through a slide-valve operated by levers and cranks in connection with the bellows and index. The slide-valves prevent the return of the measured gas to the bellows, and open and close alternately with the supply-valves to the bellows. The leather of the bellows sometimes becomes clogged with gas liquor, or stiff with the moisture, but the commonest cause of failure is an escape at the index, owing to the stuffing-boxes being worn out. When the bellows become fixed, the index is also fixed, as the movement of the bellows caused by the pressure of the gas is communicated to all parts, and, although the whole of the movement may be stopped, there may be a small supply of gas through leaky stuffing-boxes and valves. Dry meters will work when fixed unevenly, but they are much better when fixed level. Dry meters are not affected by frost.
The dry meter supplies the gas at the outlet in the same condition as it receives it. This can hardly be said of the wet meter, as the water in it becomes anything but sweet; and it is just possible that, if a little more attention were paid to the periodical renewal of the water in wet meters, the air of gas-lighted rooms would be considerably improved.
The water in wet meters may freeze during frost, and a slight thickness of ice across the surface and on the sides is sufficient to hold the drum fast. The manner of applying heat to thaw the ice within a wet meter will depend upon the position of the meter. In some cases hot water can be used internally and externally; in others, flannels dipped in hot water; and, where water cannot be used, hot sand may be placed on and around the meter; and if sand is not available, use bags of salt. Hot bricks may be placed against the meter, but are not recommended, as at least one death has resulted from their use. Bricks are easily heated until they are red-hot, and when placed against the front of meters having tinned-iron cases, the soldered seams are melted.
Where the gas-mains are below the reach of frost, the incoming gas usually a. Spindle in communication with dial; b. the leather of the bellows when closed: C, brase guide and support to bellowi; D, tin plate keeps the water in the meter from freezing, if it is not exposed to a frosty current of air, so that with deep mains, and the meter protected by a wood casing filled with saw-dust or hair-felt, it will be safe from frost Where the gas-mains are above the ground, they should be well protected by being wrapped with hair-felt or other good non-conductor, to prevent the gas from being chilled to such an extent as to absorb the heat from the water in the meter as it passes through, thus causing the water to solidify during the time it is in use. In such cases the ice will be broken in pieces as soon as formed, but the accumulation will soon be sufficient to prevent the drum revolving and supplying gas. A layer of glycerine on the surface of the water in a wet meter is good to prevent loss of heat from the surface when the meter is at rest.
Fig. 641 -Sectional Elevation of Dry of Gas meter.
Name of Meter.
size of Inlets and outlet*
Number of Light* allowed.
The sizes of gas-meters are known by the number of lights, as given in the first column of the Table XXXIX., which are standard numbers for all kinds of gas-meters regardless of their shape or class. The sizes of the inlets and outllets given in the second column correspond with the quantity of gas passing through meters of the several capacities. The figures in the third column give the maximum number of lights that may be supplied by any of the meters without interfering with their correct working. All meters from 10 lights upwards are capable of supplying at least double the number of jets, a 10-light meter being able to supply 28 separate jets, and a 100-light meter 200 separate jets. The figures in the first and third columns are enforced in order that the sizes of meters and pipes shall be based upon the number of jets.
For economical working, the gas-meter should always be as small as possible, in order to thoroughly break up the pressure from the mains when the meter is not being worked up to its total capacity, and without causing the lights to fluctuate. At the same time, care must be taken in places where a good steady light is necessary, to have the meter large enough to allow of a slight decrease of pressure in the street-main, without interfering with the supply of gas passing through, and in such cases the total number of lights should not exceed the numbers given in the third column of the table, and special main gas-governors and governor-burners should be used.
Up to 100 lights the connections to the meters are by means of brass unions, and from 100 lights upwards the connection will be by bolted flanges.
The stamping fees vary with the size of meter, being the same for all makes. Meters bearing the stamp may be fixed anywhere, notwithstanding any rules of gas companies to the contrary; but it is unwise to compel any company to accept meters they object to, as the company will take care that such meters always have something wrong with them, and will make them very costly. When meters are condemned, the seals are broken and the meters are sent to the repairing shop, and are afterwards tested and restampecL
The durability of meters varies according to their size. Small meters generally work from eight to twelve years before they need repairs, and last from fifteen to twenty years. The larger sizes (from 50 to 200 lights) last much longer, but much depends upon the position in which they are fixed, and the amount of work they have to do.