Double Block Bleed and Blind

Double Block Bleed and Blind: A complete positive isolation solution in one device

Onis Double Block Bleed and Blind (D3B) is a complete positive isolation solution in one device including one upstream valve, one quick action line blind and one downstream valve. The mechanical safety interlock between the Line Blind and the valves prevents any operation of the Line Blind if the valves remain open, there is no risk to operate under pressure. This patented safety device was design to avoid operational risk related to human factor in congested area and critical applications.

Technical sheet

Onis double block bleed and blind - D3B

Why using a D3B?

Safety procedure during piping blinding / deblinding operations require every time minimum 3 steps :

  • Shutt off the upstream and downstream valves of of the blinding / deblinding device which can be spade or figure 8
  • Depressurize the pipe by open the drain port upstream and downstream
  • Drain the liquid from the pipe if any

When these 3 steps are done proceed to the unfasten of the flanges’ fasteners (bolts and nuts).

Unfortunately human mistake by operating wrongly the valve or selecting the wrong valve, can generate pollution and more dramatical incidents and injuries in case of opening a pipe to the atmosphere without stopping the flow and depressurizing the pipe.

Sometimes the quantity of lost and wasted product between the valves and the pipe blinding device is important and has to be treated or can affect the environment if not collected.

One equipment developed by ONIS answers to safety and environmental requirements during piping blinding operation: ONIS D3B

How it works

The upstream and downstream ball valves are connected to the flanges of the ONIS line blind.

Drains ports are drilled directly in the thickness of the ONIS Line blind’s flanges.

A mechanical interlock avoid operating the lever of the line blind which permit spreading the ONIS’ seats while opening the pipe to the atmosphere and release the slide gate for translation.

For example : Fluid is passing through the equipment

To isolate the pipe proceed as hereafter :

  • Shut off the upstream and downstream valve
  • Open the bleeder ports in order to depressurize and drain the dead volume captured between the two valves which it is the smallest possible volume by design.
  • Move the interlock mechanism
  • Proceed to the operation of the ONIS line blind, blind pipe and go back to clamp ONIS’ seats position;
  • Move backward the mechanical interlock in order to secure the blinding position

In less than 1 minute, you perform a positive isolation without any tool and drain the shortest wasted volume which can be imagined without any mistake.

ONIS D3B reduces by 80% the risk of potential human mistake during blinding operation.

Onis Double block bleed and blind - components details

Technical specifications

All Double Block Bleed and Blind are designed following these specifications:

  • Forged bodies
  • Spreading design with no internal mechanism
  • Only four gaskets located on the slide gate
  • Perfect sealings – 100 % full bore


Onis Double block and bleed - technical dimensions

For any others ratings or design conditions fill free to contact ONIS.


ONIS Hisafe

The HiSafe range products are a specific products line which has been designed in order to answer to all levels of safety adapted at each applications.

Starting with a simple keylock in order to manage the authorization of line blind’s operation – B1K Blind with 1 Key, this lowest level version is follow by S2S – Step to Step version.

This second level a B1K with the patented option on slide gate : the safety boss.
Safety boss is machining to avoid to the operator to clamp the seats if the slide gate is not in a correct position.
The “+” version permits to have the information of the positioning of the slide gate by reporting through a unique safety lock’s key the real position of the slide gate. Even it the line blind is disassembled by maintenance staff some poka-yoke systems avoid to make any mistake.

The flagship of this Hi-Safe range products line is the D3B, the double block and bleed and blind device : All the procedure requested to perform a positive isolation is developed in one equipment. The D3B is the association of 2 valves and a line blind interlocked with a mechanical system. For more information click on here for D3B page. With the D3B+, the bleeder ports are also interlocked in order to secure the draining phase before the operation of the line blind.

Mechanized / Automated

When design conditions, safety or project required the ONIS devices can be motorized in order to facilitate the handling of the ONIS equipment.

Pneumatic, hydraulic or electrical actuators can be adapted on any ONIS device.
Automation can also be adapted with live reporting to the local or remote control room.
So, perform a remote positive isolation, rupture disc change or filter replacement is available with ONIS technology.

Custom designs

For each equipment, design conditions and media are requested in order to check the compatibility or the design of ONIS equipments.

Even if ASME Code is used for calculation and design, any project of customers’ specifications can be followed on demand as :

  • Materials
  • Specific design for congested area
  • Welding overlay
  • Weight restriction
  • Explosion proof requirement
  • Specific limit switches
  • Motorization
  • Firesafe

And so, ONIS engineers team are available to define with the end user the specifications and performance objectives

pictures (2)
Onis device firesafe test bench

High performance services for multiple applications

Frequently Asked Questions

How manage the pipe's depressurization if upstream or downstream valves are close to ONIS device ?

ONIS devices can be supplied with integrated drain ports already drilled into flange or half bodies. ONIS D3B device is -equipped by design with bleeder ports -permits to have the smallest dead volume the valves and the line blinds.

How can I be sure that there is no risk when I operate an Onis?

Different levels of safety are available : from operator’s training to safety optional devices as safety locks, pressure gauge, ONIS engineer can support you to choose the best solutions sum up within HiSafe range products line which is a specific line dedicated to reduce the human factors.

Do we need to depressurize the pipe before operating an ONIS device ?

As for a traditional blinding operation, safety requirements are the same. Only the way and the time request to open the pipe to the atmosphere is very reduced. Please have a look on video “How to operate a line blind” in media center page

Can you provide a solution without opening to the atmosphere?

It is not the philosophy of ONIS products because it is no more positive isolation.Indeed, in case of failure of the slide gate’s sealing, the risk is to have a leak from upstream to downstream and so to have non-safe isolation. Please have a look at “The different level of isolation.”

Do the ONIS line blinds are fire safe design ?

Yes fire safe design is available. Even if API 607 is not applicable strictly to ONIS line blinds, ONIS company is equipped with its own fir test bench and all the tests have been followed by a third part SGS or DNV.

What makes ONIS technology unique ?

no appreciation by the operator: ONIS design is set in our workshop for all lifespan in order to guarantee the tightness