Introducing the GROTH 12-TH Thief Hatch

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Storage Tank- Gauge Hatches


The GROTH Model 12-TH Thief Hatch was designed to out perform the competition, with industry leading high flow rates and precision tolerances to provide a superior sealing performance.

Storage Tank- Gauge Hatches


The leakage is less than 1 SCFH of air @ 90% of the set pressure.

Why Thief Hatches are required?

Because we always make sure that:

Protect your tanks

Protects tank from overpressure/vacuum when sized properly.

Meet industry compliance

Minimizes evaporation emissions.

Features & Benefits

Superior Sealing Performance

  • Precision machining and manufacturing to accomplish superior sealing.
  • Ultra-tight sealing reduces product leakage and fugitive emissions.
  • Active envelope pressure gasket that expands around the base to increase seal
Storage Tank- Gauge Hatches
Storage Tank- Gauge Hatches

Industry Leading Flow Rates

  • Higher flow capacity to protect from excessive pressure build up.
  • Precision machining and manufacturing to accomplish high flow rates

Direct Replacement & Easy Maintenance

  • Direct replacement for any standard round API 12 thief hatch.
  • Designed for easy maintenance, thus reducing downtime and lowering operational cost.
  • Incorporates a mechanical lock system to be used with a pad lock or lock out bar
Storage Tank- Gauge Hatches

Technical Details

  • Size: 8” (200 mm)
  • Bolting: API 12
  • Available Pressure Settings: 4, 6, 8, 12, 16, 24 & 32 osig
  • Available Vacuum Settings: 0.4, 0.9 & 3.5 osig
  • Leak Rate: 1 SCFH air @ 90% of set pressure
  • Materials of Construction: Casting: Aluminum (Non-Sparking), Envelope Gasket: HNBR, FKM, or Fluorosilicone, Vacuum Diaphragm: HNBR, FKM, Fluorosilicone, or Fluoropolymer
  • Optional: Polyester/PTFE Coating
  • Accessories: Flange (base) Gasket, Mounting Kit


Flow Curves

 Assentech supply, install and service full range of storage tank and fluid transfer equipment in the UK and Europe.

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