This document provides an overview of various boiler fittings that are essential for safe and productive boiler operation. It discusses safety valves, gauge glasses, low water cutoffs, stop valves, non-return valves, and blowdown valves. Safety valves prevent overpressurization, gauge glasses indicate water level, low water cutoffs shut down boilers if water is too low, stop and non-return valves control steam flow, and blowdown valves remove impurities from boiler water. The document describes the construction, operation, testing, and maintenance of these important boiler fittings.

1. Boiler fittings
Introduction
Boiler fittings are an integral part of a boiler. Without these essential fittings a boiler is
neither safe nor productive. Boiler fittings are essential to meet the needs of a demanding
industry which depends on safety and productivity, especially the process and power
generation industries. Some of these major fittings are- safety valves, gauge glasses,
boiler stop valves and Non return valves. All these fittings make a boiler much more
capable than ever. The construction and operation of these fittings mentioned above will
be discussed in detail below.
A safety valve is the most important safety fitting on the boiler. The safety
valve prevents dangerous pressurization of the boiler and it is essential when other
pressure safety controls fail. The safety valve should be kept free of debris and should be
tested regularly. The valve itself on a safety valve is by a heavy coil spring. The pressure
relieving capacity of the valve can be adjusted by putting a nut up or down and this can
be adjusted by increasing or decreasing the compression of the spring. A locknut is used
to prevent the adjusting nut from moving. After this process, the cap is put up and the
boiler inspector attaches his seal. This is done to prevent access to the nut. One of the
most important points to note is that, a safety valve should be connected without any
other valves or connections near it and should be as close to the boiler as possible at an
upright position. The safety valve has a lip which is filled up with steam when the safety

2. valve starts to open. When there is sufficient steam pressure to force the spring upwards,
the valve pops wide open until the pressure drops. Basically this happens when the steam
acts on the area of the disc. When we talk about safety valves, we should talk about how
they are set up. The There are two pressures that are very important when it comes to a
safety valve, the pressure at which it opens and the pressure at which it closes. This
difference between opening pressure and closing pressure of a safety valve is called the
blowdown of the safety valve. A safety valve should close at no less than ninety six
percent of the set pressure of the safety valve. The blowdown can be adjusted by the
angular ring, ie, if the ring is screwed upwards the blowdown will be longer and if it is
screwed downwards, the blowdown will be shorter. The capacity of the safety valve
depends on the pressure of the boiler. The safety valves should be able to release all the
steam generated by the boiler, without increasing the pressure to go above six percent.
The use of safety valves are not jus limited to boilers but also superheaters, although the
requirement being that seventy five percent of the pressure relief shall be provided by the
boiler safety valve.
Now as we are aware of the importance of a safety valve on a boiler,
let’s look at another important boiler fitting. The gauge glass is another important boiler
fitting, which continuously indicates the water level in a boiler. All steam boilers are
required to have at least one gauge glass and high pressure boilers are required to have at
least two. Namely, there are three main types of gauge glasses:-
 The flat gauge glass- This type of gauge glass consists of several glass plates
bolted to a steel forged housing. These lined glass plates consists of thin sheets

3. of mica to save the glass surface from being cut into by steam and water. As far
as the construction goes, the gauge is made of a steel body which is slotted in the
centre to make space for the water. A thin sheet of mica, as explained above
protect the inner surface of the flat glass and the slot is covered on both sides by
heavy flat glass. The flat gauge glass design allows for easier observation of the
water level in the boiler.
 Bulls eye gauge glass- This type of gauge glass is used for high pressure
applications. The individual port assembly design gives the gauge glass its high
pressure sustaining capability. There are many types of bull’s eye gauge glasses,
and a specific type is the bicolour multi port bull’s eye gauge glass. This type
consists of a number of sealed circular glasses with the spotlights connected at
the back. This type of gauge glass is connected to a circulating tie bar that is
connected to the top and bottom with gauge valves and a connected drain.
 Bicolour gauge glass- This type of gauge consists of a vertically-oriented
slotted metal body with a strong plain glass to the front and the rear. The front
and rear body surfaces are in vertical planes. Behind the gauge glass body are
light sources with two quite different wavelengths, typically red and green. Due
to the different refraction of the red and green light, the liquid region appears
green to the operator, while the gas region appears red. Unlike the reflex gauge,
the glass has a plane surface which it does not need to be in direct contact with
the media and can be protected with a layer of a caustic-resistant transparent
material such as silica.

4. The gauge glass should be tested regularly to ensure
reliability and productivity. The most common method of testing a gauge glass is by
closing the gauge glass top steam valve and the gauge glass bottom water valve. This
helps in isolating the gauge glass before checking the water column. When that’s
completed, the next step is to close the bottom water valve in the column, then opening
the drain valve. This allows the steam to escape through the steam connection and the
column, proving that these are free of any blocks. After this step, close the drain valve to
the column and the top steam valve opening the column bottom water valve and the
column drain valve. When this is accomplished, the water should flow though the water
connection making thoroughly sure that the passage is clear. When this is step is done,
closing the column drain valve and opening the column top steam valve will place the
column back in service. When this step is accomplished, it’s the turn of the top steam
valve of the gauge glass to be drained. By performing this step, it proves that the top
gauge connection is free of debris. The vital step is to, close the drain after the above step
is done and to close the gauge glass steam valve, which allows the opening of the water
valve of the gauge drain valve. The water flow from the drain proves that the lower
connection is free of any blocks. And finally when all the above conditions are satisfied,
the gauge glass can be placed back in operation. Apart from testing the gauge glass,
maintaining the gauge glass is also of major consideration. The gauge glass is inclined to
corrosion due to the alkalinity of the water at higher temperatures. The maintenance
process can be started off by closing the steam and water valves on the gauge glass and
also opening the drain at the same time. While removing the glass, gasket and mica
coating, the threads on the studs should be treated with graphite. Remove any gasket

5. material by scraping the gasket off the metal. Then, clean all sides of the gauge glass and
polish the gauge glass surface really smooth. When this is accomplished, apply
molybdenum disulphide on the surfaces contacting the metal. The glass should be able to
withstand high temperatures. This step prepares the gauge to place back in service.
Continuing on, place new gaskets and put in a new mica coating and also a new glass on
the one side and install the gauge cover. Now the new gauge glass can be put in service,
but the only requirement now is that the gauge glass should be given ample time to heat
up. When the gauge is heated up, crack the steam valve and allow the steam to further
warm the glass to operating temperature. Finally, if all the demands are met and the
requirements satisfied, close the drain valve and crack open the water valve to allow the
water into the glass.
Another major boiler fitting is the low-water level cutoffs. A low
water condition occurs when the level of water within a boiler’s holding vessel falls short
of the recommended level. It can be caused by a number of things, including a leaking
pipe, malfunction or simple disrepair. A low water condition places the entire boiler at
serious risk. Without the proper amount of water, a boiler may be unable to properly
transfer the intense heat and energy to which it is subjected. The result can be explosions
and fire resulting in injury, extensive property loss, or even worse. A low water cut-off
does two things. First, it accurately detects a low water condition should it occur. Second,
it automatically shuts down the combustion operation of the boiler. This will prevent the
boiler from firing while its water level is too low to properly manage the heat and energy.
There are two main types of low water level cutoffs:-

6.  Float operated low-water level cutoff- In this type, a mercury bulb contains a
two-wire switch which controls the feedwater pump circuit while the mercury
bulb with the three wire switch contains a low water fuel cutoff and an alarm.
When the boiler water level drops, the float closes the two wire switch and starts
the feedwater pumps. It should also be noted that the water level should be above
the lowest permissible level. If the pump does not start and the drum level
continues to drop, the three wire switch shuts down the boiler. Simultaneously the
fuel solenoid valve is also shutoff when the level reaches the lowest permissible.
 Probe type low water level cutoff- There are electrodes immersed in water
which can be directly mounted on the boiler shell, on the water column or in
housing. It operates with a simple concept, ie, as long as the probes are covered
by water a current will exist between the probes. This forms a closed circuit when
a solenoid valve is energised and is closed. This allows uninterrupted flow of
current. This flow of current is interrupted when the water level falls below the
upper probe. The current flow to the solenoid valve ceases and the circuit is
opened, thus shutting off the fuel supply.
As with any other boiler fitting, the low
water fuel cut-offs should also be tested to ensure dependability and capability. As per
the requirements, the low water fuel cutoffs should be tested semi-annually and
overhauled annually. The testing is done by chocking the water supply to the boiler and
then draining the boiler while the burners are going. If the low water cutoffs are working
according to requirements, the burner should shut off when the water level reaches one

7. inch above the bottom of the gauge glass. There is also a risk of debris collecting at the
float chamber and negatively affecting the operation of the float. So, regular blow out of
the chamber is recommended.
The boiler stop valve is of great importance as this fitting
deal directly with the flow of steam from the steam generator/boiler. These valves are
found on steam outlets and is located as close to the boiler as possible. Most of the stop
valves are of the outside screw and yoke rising spindle type, which makes it easier to spot
if the valve is open or closed. There are three main types of non-return valves:-
 Gate stop valve- The basic type of gate stop valve is the outside-screw-and-
yoke with the rising spindle. The spindle rises, but the handwheel which is
carried on the yoke does not. Stop valves are used to shut off or, in some
cases, partially shut off the flow of fluid. Stop valves are controlled by the
movement of the valve stem. The locking lugs secure the bonnet to the valve
body and are put in service by lowering the bonnet into the body and turning
forty five degrees. The bonnet is then seal welded to the body and the seal
ring below the seal weld prevents stress at the bonnet joint from welding.
 Angle stop valve- The angle stop valve is a globe valve with an outside
screw and yoke construction with the rising stem. This type of valve is used
in high pressure applications and the steam flow is from the bottom – up past
the disc. Because of the high pressure application, the valve is welded. To
prevent any water from entering the steam header, this condensate is drained
off before the main valve disc is opened. This valve is also equipped with a

8. drain for removing condensate from the top of the disc when the valve is
closed.
 Globe stop valve- The major difference between the globe stop valve and the
gate and angle is that the handwheel carried on the spindle rises with it. But
like the angle stop valve the operation is very similar with the steam flowing
from the bottom between the disc and the seat. As the name suggests, the
globe valve is excellent for throttling.
When talking about stop valves, another important valve which is very similar to the stop
valve is the “non-return” valve. This valve is especially essential when two or more
boilers are tied onto a main header, which can cause major backflow problems. Boiler
non-return valve (also referred to as a Stop Check valve) is a check valve that can be
closed. This valve has a disc and stem but the stem is not fastened to the disc. When
desired the stem can be turned down to shut off flow. But when the stem is returned to
the open position the disc will not come with it unless there is pressure under the disc.
Again, this valve has varying types for different applications. Some of the major types of
non return valves are:-
 Globe non-return valve- Like the stop valve, the non return valve is very
similar in construction as the handwheel is carried on the yoke. This
handwheel is turned to raise the stem and this stem disengages the piston
which frees the valve to open when the pressure in the inlet is comparatively
greater than the pressure at the outlet. Vice-versa is done to hold the piston
against the seat which blocks the valve. This valve prevents reverse flow, by

9. implementing an equalizer connection which connects the high pressure inlet
area over the disc piston to the low pressure outlet. And when the outlet
pressure increases, this equalizer line channels more pressure to the area above
the piston which shuts the valve.
 Angle non-return valve- This valve works with the same concept as the globe
non return valve, but this valve is more sensitive to pressure differentials. If the
pressure in the boiler is comparatively more than the header pressure, the valve
opens and if the header pressure is greater than the boiler pressure then the
valve will move closed. The disc can also be close by the spindle, which acts
as a cushion.
 Spring cushioned non return valve- A resilient disc check valve with a
spring return mechanism is provided. The spring return mechanism is
contained entirely within the valve body. The springs return similar structure
which engages a back side of the disc and does not require any attachment to
the disc by way of fasteners or other mechanisms. This spring cushioning
prevents the valve from unnecessary vibrations while opening or closing.
Because of the extra force of the spring, more steam pressure is required to
open it.
We discussed extensively about the boiler fittings needed to control
pressure, water level, steam flow etc. Now let’s talk about a fitting which is essential in
controlling all the above factors. Boiler blowdown is essential in maintaining the quality
of the water in a boiler. This also affects the quality of steam and also the overall

10. productivity of the boiler. Dissolved solids and particles entering a boiler through the
make-up water will remain behind when steam is generated. During operation the
concentration of solids builds up and finally a concentration level is reached where
operation of the boiler becomes impossible. If the solid particles are not disposed off
from the boiler, they can lead to:-
 Scale formation
 Carryover
 Corrosion and
 Embrittlement
There are two main types of blowdowns:-
 Manual Blowdown- Manual blowdowns are accomplished through tapings at the
bottom of the boiler where solids settled are removed. With manual blowdowns
water level control devices and cutoff devices are kept clean of any solids
interfering with their operation. All steam boilers require manual blowdowns even
if they are supplied with automatic continuous blowdown systems or not.
 Automatic continuous blowdown- A continuous blowdown system use a
calibrated valve and a blowdown tap near the boiler water surface. Water is
continuously taken from the top of the boiler at a predetermined rate.
It is a requirement that any high pressure boiler be equipped with two blowdown valves,
in which one must be a slow opening and should have a three hundred and sixty degree
turn from fully closed to fully open and vice versa. It is also required that if the boiler is

11. equipped with a quick opening valve and a slow opening valve, then the quick opening
valve be closest to the boiler. And even when operating the blowdown valve there are
procedures to be followed. For example, the quick opening valve must be opened first
when preparing to blowdown. The slow opening valve comes second while opening and
while closing, the slow opening valve must be closed first and then the quick opening
valve. There are four major blowdown valves. They are:-
 Sliding disc valve- The sliding disc type valve is called the “quick opening” type
valve. The requirement for use of this valve is that it has to be used with a “slow
opening” type valve in a blowdown system. It is a small lever that acts on a disc
to open or close this valve.
 Seatless sliding plunger valve- This valve can be classed as a “slow opening”
type valve. It is required that this valve turns three hundred and sixty degrees
before opening and vice versa. It has a pretty simple operating method, which
involves turning the handwheel which through the non-rising stem operates
plunger ports which coincide with the inlet ports. When the handwheel is closed
the plunger lowers and the inlet ports are closed off.
 Seat and disc type valve- This type of valve again is a “slow opening” type valve
and has a rising stem which is attached to a disc which is free to rotate and sets
itself on the valve seat in the body.
 Combination valves- Combination valves are basically two valves in one main
valve body and this eliminates the need for an outside valve.

12. In conclusion it can be said that without these major boiler fittings, the boiler itself cannot
be considered commercially viable. And more importantly as it is mentioned above, the
safety and productivity of the boiler itself is exponentially increased by the deployment
of these fittings. All in all, it is fair to expect that the survival of the boiler depends on its
fittings.