Spirax Sarco DP17 User manual

IM-P100-05 CTLS Issue 17
1
1. Safety information
2. General product
information
3. Installation
4. Commissioning
5. Maintenance
6. Spare parts
7. Fault finding
1000026/16
DP17, DP17E, DP17G, DP17R, DP17Y and DP27G
Pilot Operated Pressure Reducing Valves
Installation and Maintenance Instructions
© Copyright 2018
Printed in GB
IM-P100-05
CTLS Issue 17

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1. Safety information
Safe operation of these products can only be guaranteed if they are properly
installed, commissioned, used and maintained by qualified personnel (see
Section 1.11) in compliance with the operating instructions. General installation
and safety instructions for pipeline and plant construction, as well as the proper
use of tools and safety equipment must also be complied with.
1.1 Intended use
Referring to the Installation and Maintenance Instructions, name-plate and Technical
Information Sheet, check that the product is suitable for the intended use/application.
The products listed below comply with the requirements of the Pressure Equipment
Directive (PED)and carry the mark when so required. The products fall within
the following Pressure Equipment Directive categories:
Product Group 2
Gases
DP17, DP17E, DP17G DN15 - DN40 SEP
DP17R, DP17Y and DP27G DN50 1
i) The products have been specifically designed for use on steam, air and inert
industrial gases which are in Group 2 of the above mentioned Pressure Equipment
Directive.
ii) Check material suitability, pressure and temperature and their maximum and
minimum values. If the maximum operating limits of the product are lower than
those of the system in which it is being fitted, or if malfunction of the product
could result in a dangerous overpressure or overtemperature occurrence, ensure
a safety device is included in the system to prevent such over-limit situations.
iii) Determine the correct installation situation and direction of fluid flow.
iv) Spirax Sarco products are not intended to withstand external stresses that may
be induced by any system to which they are fitted. It is the responsibility of the
installer to consider these stresses and take adequate precautions to minimise
them.
v) Remove protection covers from all connections and protective film from all
name-plates, where appropriate, before installation on steam or other high
temperature applications.
1.2 Access
Ensure safe access and if necessary a safe working platform (suitably guarded)
before attempting to work on the product. Arrange suitable lifting gear if required.
1.3 Lighting
Ensure adequate lighting, particularly where detailed or intricate work is required.
1.4 Hazardous liquids or gases in the pipeline
Consider what is in the pipeline or what may have been in the pipeline at some

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previous time. Consider: flammable materials, substances hazardous to health,
extremes of temperature.
1.5 Hazardous environment around the product
Consider: explosion risk areas, lack of oxygen (e.g. tanks, pits), dangerous gases,
extremes of temperature, hot surfaces, fire hazard (e.g. during welding), excessive
noise, moving machinery.
1.6 The system
Consider the effect on the complete system of the work proposed. Will any proposed
action (e.g. closing isolation valves, electrical isolation) put any other part of the
system or any personnel at risk?
Dangers might include isolation of vents or protective devices or the rendering
ineffective of controls or alarms. Ensure isolation valves are turned on and off in
a gradual way to avoid system shocks.
1.7 Pressure systems
Ensure that any pressure is isolated and safely vented to atmospheric pressure.
Consider double isolation (double block and bleed) and the locking or labelling of
closed valves. Do not assume that the system has depressurised even when the
pressure gauge indicates zero.
1.8 Temperature
Allow time for temperature to normalise after isolation to avoid danger of burns.
1.9 Tools and consumables
Before starting work ensure that you have suitable tools and/or consumables
available. Use only genuine Spirax Sarco replacement parts.
1.10 Protective clothing
Consider whether you and/or others in the vicinity require any protective clothing
to protect against the hazards of, for example, chemicals, high/low temperature,
radiation, noise, falling objects, and dangers to eyes and face.
1.11 Permits to work
All work must be carried out or be supervised by a suitably competent person.
Installation and operating personnel should be trained in the correct use of the
product according to the Installation and Maintenance Instructions.
Where a formal 'permit to work' system is in force it must be complied with. Where
there is no such system, it is recommended that a responsible person should know
what work is going on and, where necessary, arrange to have an assistant whose
primary responsibility is safety.
Post 'warning notices' if necessary.
1.12 Handling
Manual handling of large and/or heavy products may present a risk of injury. Lifting,

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pushing, pulling, carrying or supporting a load by bodily force can cause injury
particularly to the back. You are advised to assess the risks taking into account
the task, the individual, the load and the working environment and use the appropriate
handling method depending on the circumstances of the work being done.
1.13 Residual hazards
In normal use the external surface of the product may be very hot. If used at the
maximum permitted operating conditions the surface temperature of some products
may reach temperatures of 300 °C (572 °F).
Many products are not self-draining. Take due care when dismantling or removing
the product from an installation (refer to 'Maintenance instructions').
1.14 Freezing
Provision must be made to protect products which are not self-draining against
frost damage in environments where they may be exposed to temperatures below
freezing point.
1.15 Disposal
Unless otherwise stated in the Installation and Maintenance Instructions, this
product is recyclable and no ecological hazard is anticipated with its disposal
providing due care is taken. However, if the valve has any PTFE components, special
care must be taken to avoid potential health hazards associated with decomposition/
burning of this material.
PTFE:
-Can only be disposed of by approved methods, not inceration.
-Keep PTFE waste in a separate container, do not mix it with other rubbish, and
consign it to a landfill site.
1.16 Returning products
Customers and stockists are reminded that under EC Health, Safety and Environment
Law, when returning products to Spirax Sarco they must provide information on
any hazards and the precautions to be taken due to contamination residues or
mechanical damage which may present a health, safety or environmental risk. This
information must be provided in writing including Health and Safety data sheets
relating to any substances identified as hazardous or potentially hazardous.

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2. General product information
2.1 General description
These instructions apply to the DP17 and most derivatives including the DP17E, DP17G,
DP17R, DP17Y and DP27G.
The instructions primarily relate to the use of the DP17 on steam but can be used as a guide
when the valve is used on compressed air.
For compressed air the DP17G and DP27G are recommended which have a nitrile seal for
both the main valve and pilot valve.
Note: For additional information see the relevant Technical Information Sheets.
2.2 Sizes and pipe connections - DP17, DP17G, DP17R, DP17Y and DP27G
DN15LC (not available for type DP17G), DN15, DN20, DN25, DN32, DN40 and DN50.
Screwed BSP (BS 21 parallel) or NPT (DN15 to DN25 only).
Standard flanges:
DN15 - DN50 BS 4504 PN16 and PN25
DN25 - DN50 BS 10 Table H and ANSI 300
Available on request:
DN15 - DN50 JIS 10, JIS 16 and ANSI 150
DN15 - DN20 BS 10 Table F
DN15 ANSI 300

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0
0
50
100
150
200
100
200
300
400
232
5 10 15 20 25
0 100 200 300
Pressure bar g
Temperature °C
A
E
Steam
saturation
curve
C
F
F
B
D
Pressure psi g
Temperature °F
2.3 Pressure/temperature limits -
DP17, DP17G, DP17R, DP17Y and DP27G
The product must not be used in this region.
A-D-E Screwed and flanged BS 4504 PN25, ANSI 300, and BS 10 Table H.
A-B-C Flanged ANSI 150.
F-FThe DP17G and DP27G are limited to 120 °C.
Note: DP17, DP17G and DP27G have a variable rate conical pressure adjustable spring
fitted providing a downstream pressure range of 0.2 - 17 bar g.
DP17Y has a pressure spring with a range of 0.2 - 3 bar g.
DP17R Maximum downstream reduced pressure 15 bar g. The control pressure
signal to the pilot diaphragm must be approximately 0.7 bar above the required
reduced downstream pressure.
Body design conditions PN25
PMA Maximum allowable pressure @ 120 °C (248 °F) 25 bar g (362.5 psi g)
TMA Maximum allowable temperature 232 °C (449.5 °F)
Minimum allowable temperature -10 °C (14 °F)
PMO Maximum operating pressure for saturated steam service 17 bar g (246.5 psi g)
TMO Maximum operating
temperature
DP17, DP17Y and DP17R 232 °C (449.5 °F)
DP17G and DP27G 120 °C (248 °F)
Minimum operating temperature 0°C (32 °F)
Note: For lower operating temperatures consult Spirax Sarco.
PMX Maximum differential pressure is limited to the PMO
Designed for a maximum cold hydraulic test pressure of: 38 bar g (551 psi g)
Note: With internals fitted, test pressure must not exceed: 25 bar g (362.5 psi g)

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2.4 Sizes and pipe connections - DP17E
DN15LC (not available for type DP17G), DN15, DN20, DN25, DN32, DN40 and DN50.
Screwed BSP (BS 21 parallel) or NPT (DN15 to DN25 only).
Standard flanges:
DN15 - DN50 BS 4504 PN16 and PN25
DN25 - DN50 BS 10 Table H and ANSI 300
Available on request:
DN15 - DN50 JIS 10, JIS 16 and ANSI 150
DN15 - DN20 BS 10 Table F
DN15 ANSI 300
2.5 Pressure/temperature limits - DP17E
Pressure bar g
Temperature °C
Pressure psi g
Temperature °F
0
0
50
100
150
200
232
100
200
300
400
5 10 15 20 25
0 100 200 300
The product must not be used in this region.
The product should not be used in this region or beyond its operating range as
damage to the internals may occur.
Body design conditions PN25
PMA Maximum allowable pressure @ 120 °C (248 °F) 25 bar g (362.5 psi g)
TMA Maximum allowable temperature 232 °C (449.5 °F)
Minimum allowable temperature -10 °C (14 °F)
PMO Maximum operating pressure including saturated steam service 10 bar g (145 psi g)
TMO Maximum operating temperature 190 °C (248 °F)
Minimum operating temperature 0°C (32 °F)
Note: For lower operating temperatures consult Spirax Sarco.
PMX Maximum differential pressure is limited to the PMO
Designed for a maximum cold hydraulic test pressure of: 38 bar g (551 psi g)
Note: With internals fitted, test pressure must not exceed: 25 bar g (362.5 psi g)

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Note: Before actioning any maintenance programme observe the 'Safety
information' in Section 1.
Referring to these Installation and Maintenance Instructions, name-plate and
Technical Information Sheet, check that the product is suitable for the intended
installation.
3.1 Supply
DP17, DP17G and DP27G (Fig. 1)
These are supplied ready for fitting and have a variable rate conical pressure spring suitable
for a downstream pressure of 0.2 - 17 bar (3 - 247 psi).
DP17Y (Fig. 1)
The DP17Y is supplied as the DP17, but has a lower rate pressure adjustment spring for a
downstream pressure range of 0.2 - 3 bar (3 - 44 psi).
Pressure adjustment spring
Internal pressure control
pipe assembly
Pressure setting adjustment screw
Lock-nut
Alternative recommended
downstream pressure control
pipe connection (refer to
Section 3.8, page 14)
Fig. 1 DP17, DP17G and DP17Y
3. Installation

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DP17E
The DP17E (Fig. 2) is supplied as for the DP17 with a control spring but the maximum
pressure is limited to 10 bar g (145 psi g) due to the addition of the solenoid valve. A solenoid
operated valve is fitted in the pipe between the pilot valve and the main diaphragm chamber
and is thus in series with the normal pilot valve.
The purpose of the solenoid valve is to override the pilot valve thus causing the main valve
to shut-off. It can be controlled by any device capable of interrupting the supply of current
to the solenoid coil.
The solenoid is arranged to open the valve when the coil is energised so that whatever
switching device is used it must be arranged to break the current to close the main valve.
In this way the unit will always 'fail-safe' i.e. will close the main valve in the event of a failure
in electrical supply.
Electrical supply
It is important that the solenoid is connected to the correct voltage. Therefore always check
on the supply details which are stamped on the solenoid valve name-plate before attempting
to connect up.
Electrical connection is by cable plug to DIN 43650. All wiring, connectors, etc. in close
proximity to the valve should be of heat resisting type and comply with local and national
electrical codes.
Earth
The solenoid valve should be adequately earthed.
Solenoid valve
Fig. 2 DP17E

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Fig. 3 DP17R
DP17R
The DP17R (see Fig. 3) is supplied ready for fitting. Downstream pressure can be adjusted
remotely by a controlled air supply to the pilot diaphragm chamber. The actuating air supply
must be at a pressure approximately 0.7 bar g (10 psi g) above the required downstream
pressure and controlled through a metal bodied self-relieving regulator. A check valve
should be fitted to prevent steam entering the air system, in the unlikely event of a failure
of the pilot diaphragm. Any filter should be fitted with a metal bowl and should preferably
be on the upstream side of the check valve.
The actuating air supply controlled by the regulator should be connected to the union fitting
attached to the air control block as in Fig. 4. The air inlet connection is suitable for 6 mm
O/D copper tube. The maximum reduced pressure available through the DP17R is
15 bar g (218 psi g). Typical installation is shown in Fig. 9, page 17.

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Pressure
control
pipe Small bore
drain
Strainer with 100 mesh
stainless steel screenSeparator
Steam
supply
Spiratec
sensor
chamber
Float type
steam trap
Pressure
reducing valve
DP17 and DP17E
0.9 m, (3 ft) or 15 pipe
diameters clear on either side
See Section 3.6, page 13.
Downstream isolating valve to
provide no-load conditions for
setting pressure reducing valve
Safety
valve
Discharge
pipe
Ball valve
Check
valveStrainer
3.2 Fitting (Figs. 4, 5 and 6)
The valve should always be fitted in a horizontal pipeline with the main diaphragm chamber
below the line (Fig. 4). To meet high capacities or widely varying loads, or where stand-by
facility is required, two or more valves may be used in parallel (Fig. 5). For pressure turndown
in excess of 10 to 1 consideration should be given to using the two valves in series. To
avoid instability pipework volume between the valves should be equivalent to at least 50
pipe diameters in length of the intermediate correctly sized pipework. To ensure adequate
drainage of the space between the two reducing valves a trap set should be fitted as shown
in Fig. 6.
Separator
Compressed
air
Fig. 4 Recommended installation
Installation for
compressed air
(DP17G and DP27G)
Compressed
air trap
DP17R
Compressed
air
Regulator
Filter
Float type
steam trap
Alternative for
draining separator
Strainer Sight glass
Ball valve

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Fig. 5 Two pressure reducing valves in parallel
Steam supply
]See Section 3.6
3.3 Pipeline sizing
The piping on both sides of the valve must be sized so that velocities do not exceed
30 m/s (98 ft/s). This means that a properly sized valve will often be smaller than the
connecting pipework.
3.4 Pipeline stresses
Line stresses caused by expansion or inadequate support should not be imposed on the
valve body.
3.5 Isolating valves
These should preferably be of the full bore type.
3.6 Removal of condensate
It is recommended that a separator with trap set is fitted upstream of the valve to ensure
dry steam conditions.
If there is a rise in the low pressure line from the valve then a further drain point should be
provided to keep the valve drained after shutdown.
Steam supply
]See Section 3.6
Fig. 6 Two pressure reducing valves installed in series
]
]
]

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3.7 Protection from dirt
The valve should be protected by a pipeline strainer with 100 mesh screen. The strainer
should be fitted on its side to prevent the accumulation of water. The strainer screen should
be examined and cleaned at regular intervals.
3.8 Pressure control pipe
For applications that require closer control, improved stability or maximum capacity condition
the internal pressure control pipe should be replaced by an external pressure control pipe
as follows:
Remove the internal pressure control pipe assembly.
The resulting " BSP tapping in the side of the body should be blanked using the plug
provided in the linen bag attached to the valve (which also contains the fitting instructions).
The other " BSP tapping in the side of the pilot valve chamber, should be blanked off using
the plug fitted in the tapping provided on the front of the pilot valve chamber. Into this latter
tapping, fit the brass compression fitting with brass compression ring which is also contained
in the linen bag. This is suitable for the fitting of 6 mm O/D pipe. If suitable pipe is not
available the compression fitting can be removed and ¼" nominal bore steel pipe screwed
directly into the pilot valve chamber.
The pressure control pipe should be connected into the top of the reduced pressure main
at a point where in either direction there is a length of straight pipe uninterrupted by fittings
for at least 1 m (3 ft) or 15 pipe diameters whichever is the greater. It should be arranged
with a positive fall so that any condensate can drain away from the DP17. Where the size
of the reduced pressure main makes it difficult to maintain a fall when entering the top of
the main, the pressure control pipe may be connected in the side of the main.
3.9 Pressure gauges
It is essential to fit a pressure gauge on the upstream and downstream side so that the
valve can be properly set and monitored.
3.10 Bypass
Information regarding bypasses:
It may be necessary to ensure that primary fluid flow continues in the event of the main
control failing. This is often achieved by fitting a bypass around the control valve assembly.
A better option is a duplex valve assembly, installed in parallel with the main valve, as a
manual bypass cannot accurately control pressure/flow/temperature without constant
manual supervision. Conversely, a duplex control station will provide proper control, should
the main valve ever need to be removed.
Although not recommended, if a manual bypass valve is fitted, the bypass valve flow
coefficient (Kvs) should be the same as, or near to that of, the control valve. This means
that the manual valve and control valve could have different connection sizes. The bypass
valve should also be capable of throttling not just isolating, to reduce wear on the valve
when in service and to facilitate manual control.
Ideally, any bypass pipework should be arranged either above or alongside the main
assembly. On steam systems, it should never be below it.

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3.11 Safety valve
A safety valve should be fitted to protect the downstream equipment from excessive
pressure. It should be set to lift below the safe working pressure of the downstream
equipment, and will normally be sized to pass the full capacity of the PRV should the PRV
fail in the fully open position. The safety valve set pressure should take account of its reseat
characteristic and the 'No-load' pressure setting of the PRV. For example, the typical
blowdown value (reseat differential) for a DIN type safety valve is 10% of set pressure. The
minimum possible safety valve set pressure must therefore equal the no load set pressure
of the reducing valve plus the blowdown value of the safety valve plus a small margin of at
least 0.1 bar. If the set pressure is any lower, if whatever reason the safety valve lifts it will
not shut properly and will simmer, creating a leak which is often wrongly diagnosed as a
result of a leaking reducing valve.
Discharge pipework should be taken to a safe place.
3.12 Position in relation to other control valves
Line or system isolation valves (A), either remotely actuated or manual, should be installed
on the upstream side of the DP17 reducing valve.
Where there is downstream control equipment (B), particularly when it is fast acting
(for instance pulsed piston actuated valves) ensure the control equipment is at least 50
pipe diameters away from the DP17 to prevent pressure pulses being transmitted back
causing unstable operation and premature wear or if this is impractical an intermediate
vessel can provide a similar benefit.
Where a safety valve (C) is required to protect the system downstream of a DP17 and where
a control valve is also being used downstream of the DP17, it is recommended that the
safety valve is fitted downstream of the control valve rather than in between the DP17 and
the control valve. If any slight leakage occurs this will avoid any pressure build-up causing
nuisance operation of the safety valve but provide complete protection for the downstream
system.
Where valves are installed downstream of the DP17 (B) the intermediate downstream
pipework must be properly trapped (D) to ensure no condensate can buil up on the
downstream side of the DP.
Fig. 7 DP17 position in relation to other control equipment
D
C
B
A
A

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WARNING
Direct injection systems
This product contains a rust inhibitor to protect it against corrosion during
storage. To avoid any possible contamination of your product, after first blowing
down the approach pipework, we recommend that the valve is blown through
thoroughly in order to remove any trace of the inhibitor.
4. Commissioning
DP17, DP17E, DP17G, DP17Y and DP27G (Fig. 8)
2. Close all valves at reducing valve station,
including valves on bypass line if fitted.
3. Check that adjustment screw is turned fully
anticlockwise until spring is slack.
DP17R (Fig. 9)
2. Close all valves at reducing
valve station, including the valve
on the bypass line, if fitted.
3. Check that the actuating air
supply is off and the pressure is
zero.
4. Check that the pressure gauge isolating cocks are open.
5. For correct operation of the valve it is important that the pilot and main valves are not
subjected to dirt or other hard particles. Therefore, prior to bringing the valve into
operation, ensure that the upstream pipework has been cleared of all loose dirt and
hard particles and that the main strainer screen is examined and cleaned if necessary.
6. Slowly open the upstream isolating valve until it is fully open.
DP17, DP17E, DP17G, DP17Y and DP27G
7. Using a 19 mm A/F spanner slowly turn
adjustment screw in a clockwise
direction until desired downstream
pressure reading is obtained.
8. Holding the adjustment screw in position
with the spanner tighten down the lock-
nut to secure the setting of the
adjustment spring,making sure that the
'C' washer stays in position.
DP17R
7. Slowly admit actuating air through the
pressure regulator until the desired
downstream pressure is obtained.
Note : To facilitate resetting of the reducing
valve it may be desirable to position the
downstream pressure gauge at a viewpoint
close to the air regulator.
If this necessitates fitting the pressure
gauge below the steam line, the
interconnecting pipe should be drained at
the low point otherwise the gauge will give
a false reading.
9. Slowly open the downstream valve until it is fully open.
Note: After installation or maintenance ensure that thet system is fully functional. Carry
out tests on any alarms or protective devices.
4.1 Setting procedure (Fig. 8 and Fig. 9)
1. Ensure that all connections are properly made and that all valves are closed.

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Fig. 8 Setting procedure sequence DP17, DP17E, DP17G, DP17Y and DP27G
Fig. 9 Setting procedure sequence DP17R
4.2 Two or more valves in parallel
When more than one reducing valve is used it is an advantage to use two valves of unequal
size, the smaller one being chosen to meet the lower load requirements and the larger valve
to come into operation so that both meet the normal and maximum demand.
It is necessary to commission each valve independently (one at a time) following the
procedure detailed in Section 4.1 but setting the smaller valve at a pressure higher than
the larger valve.
]See Section 3.6, page 13
2
5
2, 9
2, 6
5
3, 7, 8
44
Condensate
return
Steam flow
Optional bypass line (see Section 3.10)
]
2
5
2, 9
32, 6
5
44
Condensate
return
Steam flow
Optional bypass line (see Section 3.10)
]See Section 3.6 page 13
]

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5. Maintenance
Note: Before actioning any maintenance programme observe the 'Safety
information' in Section 1.
Warning:
The body gasket (all DP17 derivatives) and actuating chamber gasket (DP17R)
contains a thin stainless steel support ring which may cause physical injury if not
handled and disposed of correctly.
5.1 Routine maintenance
It is recommended that the valve is dismantled once every twelve to eighteen months for a
complete overhaul and ideally this should be carried out with the valve removed from the
line. The following parts should be inspected and refurbished or replaced as necessary:
- Main valve seat and valve head.
-Pilot valve chamber assembly.
-Main valve screen.
-Main diaphragms.
-Pilot diaphragms.
Pilot diaphragms
Main
diaphragms
Main valve seat
and valve head
Main valve screen
Pilot valve
chamber assembly
Body gasket
(see warning above)

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To renew or change the control spring
It is not necessary to isolate the valve in order to change
the spring.
1. Release the lock-nut.
2. Turn the adjustment screw anticlockwise. Ensure there
is no compression on the pressure adjustment spring.
3. For the DP17 and derivatives only - Slide out the
'C-shape' washer.
4. Remove the cover.
5. For the DP17 - Remove the pressure adjustment spring
and top plate.
For the DP27G - Firstly undo the 4 off spring housing
securing nuts and remove the spring housing. Then
remove the pressure adjustment spring and the top
spring plate.
6. Reassemble in reverse order.
To renew the pilot valve assembly
DP17, DP17E, DP17G , DP17Y and DP27G
Isolate the pressure reducing valve and zero the pressure.
Follow Steps 1 to 5 then proceed.
DP17R
Isolate the actuating air supply and zero the pressure.
7. Unscrew the unions and release the pipework.
8. DP17, DP17E, DP17G and DP17Y
Unscrew the spring housing nuts and remove the spring
housing, bottom spring plate and diaphragms.
DP27G
Undo the 4 off spring housing securing nuts and
remove the spring housing. Then removethe pressure
adjustment spring, top spring plate, bottom spring plate
and diaphragms.
DP17R
Unscrew the securing nuts and remove the air control
block and diaphragms.
DP17
DP27G
DP17
2
1
3
5
4
8
7
7
1
4
5
7
7

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9. Remove the pilot valve housing.
10. Ensure that the main valve return spring is still in position. Any trapped dirt or scale
should be removed from the pilot valve assembly. If appropriate, the complete pilot
valve chamber assembly can be refitted following Steps 14 to 21. If necessary, the
complete pilot valve chamber assembly should be replaced as follows:
Note: The pilot valve assembly is no longer available as a standard spare. Because of
the difficult process described in Step 13, it has now been discontinued. The complete
pilot valve chamber assembly is the recognised spare. However for customers with pilot
valves only still in stock, these can be used by following Steps 11-13. This assembly
contains 2 off PTFE seals. The following handling precautions should be observed.
Handling precautions for PTFE
Within its working temperature range PTFE is a completely inert material, but when
heated to its sintering temperature it gives rise to gaseous decomposition products or
fumes which can produce unpleasant effects if inhaled. Fumes can be produced during
processing: for example, when the material is heated to sinter it, or when brazed
connections are being made to cable insulated PTFE. The inhalation of these fumes is
easily prevented by applying local exhaust ventilation to atmosphere as near to their
source as possible.
Smoking should be prohibited in workshops where PTFE is handled because tobacco
contaminated with PTFE will during burning give rise to polymer fumes. It is therefore
important to avoid contamination of clothing, especially the pockets, with PTFE and to
maintain a reasonable standard or personal cleanliness by washing hands and removing
any PTFE particles lodged under the fingernails.
11. Unscrew and remove the pilot valve assembly (22 mm A/F)
12. Screw the new pilot valve into the housing. Torque 45 - 50 N m (33 - 37 lbf ft).
13. Check that there is a very slight clearance between the top of the plunger and a straight
edge placed across the diaphragm location recess. (N.B. Because of production
tolerances the plunger is supplied slightly longer than is always required and it will
generally be necessary to grind or machine material off the top end to give the correct
length). After machining make sure the sharp edges are removed from the top of the
plunger as these could damage the diaphragm.
14. Remove the screen and clean. Ensure that the gasket faces are clean.
15. Ensure that the main valve return spring is still in position.
16. Fit new gasket.
17. Replace the screen. Assemble the pilot valve housing.
18. Refit the two diaphragms making sure that they are fitted the same way round as they
were removed and that all contact faces are clean. Diaphragms showing signs of wear
or damage should be replaced.
19. DP17, DP17E, DP17G, DP17Y and DP27G
Replace bottom spring plate.