IMPROVEMENTS IN SPRINGS FOR SAFETY VALVES AND OTHER PURPOSES
Year: 1877

page_text: "
LETTERS PATENT to Martyn John Roberts, of the City of Bath, Esquire, for
the Invention of IMPROVEMENTS IN SPRINGS FOR SAFETY VALVES AND
OTHER PURPOSES."
Sealed the 29th September 1877 and dated the 3rd April 1877.
PROVISIONAL SPECIFICATION left by the said Martyn John Roberts at the
Office of the Commissioners of Patents on the 3rd April 1877.
MARTYN JOHN ROBERTS, of the City of Bath, Esquire.
SPRINGS FOR SAFETY VALVES AND OTHER PURPOSES."
"IMPROVEMENTS IN
My improvements consist in so forming spiral or helical springs, as to be contained
within a small compass, and yet permit of their being considerably extended or
compressed without presenting that large amount of resistance to such change of
form which obtains in the springs at present in use for safety valves and other
purposes. Supposing for example that a spiral or helical spring of the ordinary
form be compressed in its length to the extent of four inches, in order to obtain a
spring force of 100lbs., and as in a well formed spring equal compressions produce
equal forces, the compression of the said spring another inch would involve an
increased force of 25lbs., which increase at the outer end of a safety valve lever
would be a serious evil, as it would prevent the valve lifting until a dangerous steam
pressure in the boiler existed. Therefore it is highly desirable that the usual rise
of an inch in the outer end of a safety valve lever, and a like extension or compres-
sion of its spring should be followed by a minute amount only of increased resistance
in the spring.
To obtain this object and get an increased resistance in the said spring of, say,
1lb., only for the extra compression of an inch, it will be necessary that the normal
compression of the spring is 100 inches; and as the initial length of a spring is
generally at least three times the amount of its compression, such a spring must be
24 feet long, which is a length quite inadmissible for locomotive boilers or any
ordinary machinery. But I obtain the desired end by forming a spring in a series
of lengths, one within the other, these separate lengths being so attached to each
other as virtually to form one continuous spiral of any desired number of convolutions.
Suppose the length of the compound series to be restricted to, say, 18 inches, I first
[Price Bd1

page_text: mako a spiral coil of 18 inches long (which I will call No. 1), then on the outside
of this and about concentric with it, I make another coil (No. 2), outside this again
another (No. 3), and so on until the, required number of spirals is obtained. Then
the ends of the several spirals are fixed to those next adjoining at opposite ends of the
spring alternately. The action will be, say, that No. 1 is compressed, No. 2 extended,
No. 3 compressed, No. 4 extended, and so on, and as the sum of the total compres-
sion and extension of the separate coils or convolutions in the spirals is the amount
afforded by the entire apparatus, an apparatus consisting of a number of con-
volutions compressed and extended altogether 100 inches, and giving a force of
100lbs., would only offer the resistance of one pound to the extension or compression
of another inch. If such apparatus were placed directly on the back of a safety
valve, where the lift of the valve seldom exceeds 10th of an inch, the same arrange-
ment would still suffice; and for cylinder escape valves, the slight opposition given
by the apparatus to their full opening is of great importance, especially for marine
engine cylinders, where dead weights cannot be used to advantage.
In order to prevent the motion of one spiral interfering with the action of another,
I sometimes place a cylinder of generally some thin material between one spiral
and another, and this prevents the locking of one convolution with another or
otherwise checking its proper action.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Martyn John Roberts in the Great Seal Patent Office on the 3rd
October 1877.
MARTYN JOHN ROBERTS, of the City of Bath, Esquire. "IMPROVEMENTS IN
SPRINGS FOR SAFETY VALVES AND OTHER PURPOSES."
My improvements consist in so forming spiral or helical springs as to be contained
within a small compass, and yet permit of their being considerably extended or
compressed without presenting that large and accumulative resistance to such change
of form which obtains in the springs at present in use for safety valves and other
purposes. Supposing, for example, that a spiral or helical spring of the ordinary
formn be compressed in its length to the extent of four inches, in order to obtain
a spring force of 100lbs., and as in a well formed spring equal compression produces
equal forces, the compression of the said spring another inch would involve an
increased force of 25lbs., which increase at the outer end of a safety valve lever
would be a serious evil, as it would prevent the valve lifting until a dangerous steam
pressure in the boiler existed. Therefore it is highly desirable that the usual rise
of an inch in the outer end of a safety valve lever, and a like extension or compres-
sion of its spring should be followed by a minute amount only of increased resistanco
in the spring.
To obtain this object and get an increased resistance in the said spring of, say,
1lb. only for the extra compression of an inch, it will be necessary for the normal
compression of the spring to be 100 inches, and as the initial length of a spring
is generally at least three times the amount of its compression, such a spring must
be 24 feet long, which is a length quite inadmissible for locomotive boilers or any
ordinary machinery. But I obtain the desired end by forming a spring in a series
of lengths, one within the other, these separate lengths being so attached to each
other as virtually to form one continuous spiral of any desired number of con-
volutions. Suppose the length of the compound series to be restricted to, say,
18 inches, I first make a spiral coil of 18 inches long (which I will call No. 1), then
on the outside of this and about concentric with it, I make another coil (No. 2),
outside this again another (No. 3), and so on until the required number of spirals
is obtained. Then the ends of the several spirals are fixed to those next adjoining
at opposite ends of the spring alternately. The action will be, say, that No. 1 is

page_text: compressed, No. 2 extended, No. 3 compressed, No. 4 extended, and so on, and as
the sum of the total compression and extension of the separate coils or convolutions
in the spirals is the amount afforded by the entire apparatus, an apparatus consisting
of a number of convolutions compressed and extended altogether 100 inches, and
giving a force of 100lbs. would only offer the resistance of one pound to the
extension or compression of another inch. If such apparatus were placed directly
on the back of a safety valve, where the lift of the valve seldom exceeds 1th of an
inch, the same arrangement would still suffice, and for cylinder escape valves, the
slight opposition given by the apparatus to their full opening is of great importance,
especially for relief valves of marine engine cylinders, where dead weights cannot be
used to advantage.
In order to prevent the motion of one spiral interfering with the action of
another, I sometines place a cylinder of generally some thin material between one
spiral and another, and this prevents the locking of one convolution with another or
otherwise checking its proper action.
The accompanying Drawing represents in vertical section a spring constructed
according to my Invention, and applied to a safety valve of the box or chambered
form described in the Specification of my Letters Patent dated 29th August 1876,
No. 3405.
•
A is the valve, and B the valve rod; C is the first spring or coil resting on or
attached to the top of the valve; D is the second spring or coil, the top convolution
or turn d of which overlaps the first spring C; E is the third spring which is
underlapped by the bottom convolution or turn d¹ of the second spring. A fourth
spring, and more if necessary, may be added in a similar manner, and there must
be a bearing or other suitable obstruction to take the thrust of the last spring of
the series.
It will be readily understood that when the valve A rises, the first spring C
will be compressed, that the second spring D being acted against by the top
convolution of the spring C will be extended, that the third spring E being
acted against by the bottom convolution of the spring D will be compressed, and
so on.
The force of the springs may be regulated as required by means of a screw made
to act upon the support or bearing of the last spring of the series.
As before stated cylinders may be placed between the adjoining springs to
prevent their becoming locked, or their action being otherwise checked. And in
some cases it may be better to connect the proper ends of the adjoining springs to
cach other by plates instead of making the last convolution of one spring overlap
or underlap another spring, as shewn in the Figure.
Although I have shewn the valve to be provided with a guide rod B, this rod
may in many cases (and I prefer that it should) be dispensed with, particularly
where the lift of the valve is small, and the scantling or thickness of the springs is
great, and in such cases I sometimes guide the valve by means of a flexible holder
or spring as described in the Specification of my Letters Patent of 29th August
1876, and shewn at C in Figure 3 of the Drawings annexed to such Specification.
And having now described the nature of my said Invention, and in what manner
the same is to be performed, I declare that I claim constructing springs for safety
valves and other purposes, substantially as herein-before described and represented
in the annexed Drawing.
In witness whereof, I, the said Martyn John Roberts, have hereunto set
my hand and seal, this Second day of October, One thousand eight
hundred and seventy-seven.
MARTYN J. ROBERTS. (L.S.)