CAL-VAC and POS-A-SET Bursting Discs (Rupture Disc) Assemblies are highly accurate, double acting pressure relief devices designed to protect processing and storage tanks against implosion or overpressure conditions that can occur in:
Positive Pressure // overfill, external fire, steam regulator failure
Vacuum Relief // liquid pump out, insufficient flow through  sanitary vent filer, flash vacuum due to CIP cool rinse, primary vent malfunctions, blanket gas or air regulator failure.

Both designs relieve pressure settings starting as low as 1 InWC (inches water column) differential. The difference in the CAL-VAC Bursting Disc and POS-A-SET Rupture Disc is the orientation of the components to meet the relieving requirements. The CAL-VAC Rupture Disc relieves ultra low pressure in the vacuum (negative) pressure direction, while the POS-A-SET Rupture Disc relieves ultra low pressure in the positive pressure direction.


Minimum/Maximum Burst Rating at 72°F (22°C)


CAL-VAC and POS-A-SET  Bursting Discs  FEATURES:

  • Ultra Low Pressure Relief Controlled By a Girdle: As a pressure in the system approaches the burst pressure setting, the girdle becomes loaded until it deflects back past a knife blade assembly located in the holder. As the girdle passes the knife blade assembly, the seal is penetrated and cut in a triangular pattern to relieve the ultra low pressure. Refer to Table 2 for available girdle settings and maximum recommended operating pressures.
  • Higher Pressure Relief Controlled By a Top Section : The perforated metal top section, under tension loading, relieves pressure in the opposite direction than the girdle when overpressure in the system occurs. It incorporates CDC’s seven hole pattern at the apex of the Bursting Disc dome. The seven-hole pattern, along with six precut sections, provides a non-fragmenting design. Refer to Table 1 for minimum and maximum burst ratings of the CAL-VAC and POS-A-SET Bursting Disc top section. Additionally the top section’s pre-punched holes provide optimum flow through the Bursting Disc when relieving in the ultra low pressure direction through the girdle.
  • Reduce Product Build-Up and Promote Easier Cleaning: CAL-VAC and POS-A-SET Bursting Discs have a flat seat design to reduce susceptibility to product build-up and promote easier cleaning.
Nominal Size Range:
3 ” – 12 ” ( 80 mm – 300 mm )
Burst Pressure Range
2 psig- 150 psig ( 0,138 barg – 10,3 bargRecommended Operating Ratio
Within 1 inch W.C. of min. setting

Seating Configuration: Flat Seat

  Service :Liquid or Gas 

B.D.I. Alarm System Compatible? Yes 

ASME Code Symbol Stamp Available? No


You can contact us by Phone 01726 844707 , Email : or using the enquiry form below

Some of our customers testimonials

Emergency-Relief-Valve-Pilot-Operated-2500a  Assentech- pilot operated pressure relief valves service and calibration

After conducting a Third Party Witness Inspection, I was most impressed with Ewart and his team, their professionalism, and product knowledge I found to be excellent.

Ian Johnston

Director, RAK Inspection

Emergency-Relief-Valve-Pilot-Operated-2500a  Assentech- Geodesic Dome Installation

Assentech were subcontracted to assemble and install a 25m geodesic dome for Shaft G on the Lee Tunnel project. My experience with Assentech from pre-contract through to assembly has been very positive. Unlike other subcontractors I have experienced on this project, Assentech had a very positive attitude to producing the level of documentation required for a project of this scale. Leading to a high quality pre construction packaged approved in a timely manner. The communication regarding the manufacturing process was first class allowing us to easily plan our works and prepare the site. Dome assembly was carried out very efficiently and completed to programme. The task was correctly resourced and well supervised. The work force had a positive attitude and carried out the task safely. In summary from my perspective it has been a very easy subcontract to manage with a high quality finished product.

Robert Colthorpe

Site Agent – Lee Tunnel Project, Morgan Sindall

Emergency-Relief-Valve-Pilot-Operated-2500a  Assentech wins supplier excellence award from Eastman Chemicals

We were extremely pleased with the level of service and professionalism demonstrated by Assentech, right from our initial enquiry, through delivery and post installation. As a recipient of only two of these awards made by Eastman Chemical Company in the UK, based on performance in 2014, Assentech are rightly proud of their achievements.

Robert Dodgson

TH3 Project Procurement Lead, Eastman Chemical Company

Emergency-Relief-Valve-Pilot-Operated-2500a  Assentecha-IFR Installations at Vopak, Teesside

As you said “you delivered what it said on the tin”. On time and on budget.  Your up front engineering to determine the suitability of your product for our application was second to none, i have not seen anyone else in the industry pay as much attention to detail before you get the purchase order number as Assentech.

Garry Lee

Project Manager, Vopak Limited

Emergency-Relief-Valve-Pilot-Operated-2500a  Assentech-IFR Installations at Navigator Terminals

Assentech have supported our Navigator Terminal (formerly known as Vopak Teesside) on two important ~
projects by providing technical assistance and supplying and fitting a total of 11 Internal floating roofs. Both projects have been completed on schedule and on budget. Assentech have provided an excellent level of experience and front end engineering support with high quality drawings and documentation. Their specialist on site labour have worked collaboratively with us and Assentech have proven to be open, honest and flexible partners.
We have experience of both their Heavy Duty Pontoon type and Full Contact IFR’s and we continually monitor operation and performance of all lFR units Installed on site and consider the Assentech supplied Matrix brandto be the best in the market with exceptional build quality and rigidity. Our clients have inspected the installations and have always remarked upon the build quality and have been impressed with their strength in fully supporting up to four people without noticeable deformation. The design and construction of their stainless steel shoe seals continue to prove to operate excellently with no noticeable reduction in performance or flotation ability over the time since Installation.
Assentsch have proven to be extremely competitive on price and their installation and inspection activities have always been thorough. Navigator therefore have no hesitation in recommending Assentech to other companies considering their services.

Brian Beddow

Project Manager, Navigator Terminals Seal Sands