What are differences between Full Opening Safety Valve (TIW valve) and Inside BOP valve (Gray Valve)?

Two types of stabbing valves that must be prepared for well control are Full Opening Safety Valve (TIW valve) and Inside BOP valve (Gray Valve). We would like to describe what the differences between two valves are.


Full Opening Safety Valve or TIW valve

Full Opening Safety Valve or TIW valve is a ball valve designed for high pressure condition and it can hold pressure from both directions. It is called “Full Opening” because when the ball valve is opened; the flow path through the valve has a smooth inside diameter. One thing that you need to remember is that the term “Full Opening” does not mean that the ID of the valve is the same of drill pipe ID. ID of the valve is typically smaller than the pipe in the hole.

 What are differences between TIW valve and Grey Valve 1

 Figure 1 Full Opening Safety Valve

The valve should be always located on the rig floor and left in the open position. Additionally, you need to ensure that personnel on the rig have a right wrench to close the valve. The valve left in the open position is critical because the valve can stabbed quickly into drill string if the well flows through drill pipe.

For good drilling practices, you must have all size full opening safety valves which can be screwed into each size of drill pipe, drill collar, tubing, etc on the rig. When there is any string in the hole, the correct connection of the valve must be ready on the rig floor to stab in. Furthermore, it is a good practice to perform well control drill during tripping operation in order to ensure that the crew are familiar with the stabbing procedure.

 Inside BOP valve (Gray Valve)

Insider Blowout Preventer (IBOP) valve has  several industrial names as drill pipe float valves, Gray valves, Omsco valves and drop-in dart valves.

What are differences between TIW valve and Grey Valve 2

Figure 2 Inside BOP (Dart Type)

 This valve is a non-return valve (check valve) allowing pumping through the valve into the drillstring but it prevents upward flow and the more widely used type is “dart-type”. The dart is used to hold the tool open therefore it is possible to stab the valve while the fluid is flowing through the drillpipe. With the IBOP valve installed in the drill string, it allows you to strip in hole without mud flowing through the drillsting. The IBOP valve should not be used for shut the well in while tripping.


Cormack, D. (2007). An introduction to well control calculations for drilling operations. 1st ed. Texas: Springer.

Crumpton, H. (2010). Well Control for Completions and Interventions. 1st ed. Texas: Gulf Publishing.

Grace, R. (2003). Blowout and well control handbook [recurso electrónico]. 1st ed. Paises Bajos: Gulf Professional Pub.

Grace, R. and Cudd, B. (1994). Advanced blowout & well control. 1st ed. Houston: Gulf Publishing Company.

Watson, D., Brittenham, T. and Moore, P. (2003). Advanced well control. 1st ed. Richardson, Tex.: Society of Petroleum Engineers.

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16 Responses to What are differences between Full Opening Safety Valve (TIW valve) and Inside BOP valve (Gray Valve)?

  1. khalid A Hatim says:

    My Thanks

  2. lsalazar says:

    We install our fosv when doing wireline operations. Can the fosv shear the wireline if needed?

  3. hamdi says:

    what if the fosv stuck in closed position w/gases below it ?

    • Firstly, you need to kill the well in the annulus and there are few methods to kill the well for this case as volumetric + lubricate/bleed or bullheading. Once the well is secured, you need to break out and bleed off some trapped gas. This is quite tricky for this operation.


  4. Greg Leger says:

    The only way you would want to open a FOSV with pressure below, is to equalize the pressure from the top. If the pressure is unknown, apply pressure in 300 psi increments at a time, once the pressure gets close to equalizing, you can open the valve.


  5. amin allavi says:

    pls clarify the differ between FULL OPENING SAFETY VALVE & LOWER KELLY VALVE ? ?

    • Amin,

      They are the same valve but different location used on the rig. “The TIW Kelly Valve is designed to hold pressure in either direction and can be used as a Drill Stem Safety Valve or as either an Upper or Lower Kelly Cock. “

  6. PeterM says:

    Nice blog, however, an IBOP or Gray valve is completely different from a drill-pipe float valve or drop-in dart sub.

    A drill pipe float valve is a flapper-type valve installed just above the bit in the bit sub.

    A drop-in dart sub (Hydril) is installed somewhere in the string and a dart can be dropped in the string to seal-off from below but you can pump through the dart from above.

  7. Osama says:

    pretty nice and useful information , good website

  8. NEIL says:

    Would like to know what is the correct pressure testing of a grey valve, do you know where I can find
    this procedure

  9. Kong desert says:

    All of them are safety valve but the bop is a big valve specialized and the safety relief valve are parts from the bop it self

  10. Awaico Alyammahi says:

    Testing TIW or GRAY valve same rate with BOP testing pressure

  11. Juan Castro says:

    Wt limit on pulling on TIW Valve using 2 7/8 PH-6 work string 70k -170k

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