Instruction Manual

Diaphragm Seal Installation and
Maintenence Manual
© 2019 Ashcroft Inc. 250 East Main Street 06614, Tel: [phone] • Fax: [phone], All specifications are subject to change without notice.
All sales subject to standard terms and conditions. www.ashcroft.com All rights reserved. 100-200-300_seal_im_RevA_07-26-19
1. Introduction
A diaphragm seal is a device that attaches to the process side
of a pressure-measuring instrument to separate the instrument
from the process fluid while transmitting pressure across a
flexible membrane. The volume enclosed by the diaphragm,
the top housing, and the measuring element is completely
filled with a pressure transfer fluid. A change in pressure at the
process connection causes a displacement of the filling fluid
due to deflection of the diaphragm, transferring the change in
pressure to the sensing element of the pressure instrument.
2. Safety Information
WARNING: Serious injury or equipment damage can
result from failure to properly install, maintain, or
operate these components. To assure safe operation
and maintenance procedures, read carefully
and follow the instructions in this manual.
• Follow all instructions in this document to
avoid exposure to pressurized fluid
• Use proper tools and safety equipment in
installing or maintaining components
• Assure that process pressure and temperatures
are properly monitored and maintained, and the
process fluid is appropriate and compatible with
the wetted materials of the diaphragm seal
• Follow all of your company’s safety procedures in
the event of a leak or diaphragm seal failure
3. Diaphragm Seal Components
Though the exact components will vary
between specific models, most diaphragm
seals will share the same essential parts.
3.1 Top Housing
The top housing of the diaphragm seal is used to connect
to the pressure measurement instrument. The fill port allows
for assemblies to be vacuum filled, then sealed with a ball
bearing in a conical seat and secured with a set screw.
3.2 Diaphragm
The diaphragm serves to separate the process fluid from
the filling fluid, and as such is a component wetted to the
process. Diaphragms can be welded or threaded into the top
housing, which in turn can be welded or clamped to a lower
housing. Changes in pressure cause the diaphragm to deflect,
displacing fill fluid and transmitting pressure to the pressure-
measuring instrument. It is important to ensure that a
diaphragm has sufficient displacement to operate a pressure-
measuring instrument across its entire span. For detailed
diaphragm seal and instrument compatibility, see Ashcroft
Product Information Page DS-PI-82, “Minimum and Maximum
Pressures for Diaphragm Seals,” found at Ashcroft.com
3.3 PTFE Gasket
All 100- and 200-series seals are supplied with a single-
use PTFE skirted gasket. Refer to Section 4.2.3 for
process considerations related to these gaskets.
Upper Ring
(Clamping)
Top Housing
Fill Port
Flushing
Port
Diaphragm
Lower Housing
Lower Ring
(Clamping)