New regulations by the EPA (New Source Performance Standards) require owners and operators in the Permian Basin to find and repair leaks which result in fugitive emissions of both methane and VOCs. Violations have resulted in significant fines and facility shutdowns. Common compliance issues include leaking thief hatches and other mechanical relieving devices.

At a typical Permian Basin, more specifically a Delaware Basin wellsite, a mixture of oil, gas, and water is extracted from the ground through the wellhead and flow is diverted to a separator or heater treater. The mixture is separated into hydrocarbon liquids, gas, and water. The produced hydrocarbons are then sent to storage tanks, typically at atmospheric pressure and when entering the low-pressure storage tanks the gases (methane & VOC’s) in the oil flash off (released from liquid phase to gaseous phase).

Each tank in oil field batteries are equipped with a thief hatch to allow tank access (gauging, inspection, etc.) and to protect each tank from overpressure or excessive vacuum. In cases where the tanks are manifolded together going to a Vapor Recovery Unit (VRU) if each tank has a good seal at the thief hatch the gasses coming off the tanks travel down the manifold piping and to the VRU. If any of the tank thief hatches are leaking the VRU is inoperable.


  • Eliminate thief hatch leakage of methane and VOC’s.
  • Allow flashed gas to travel to the VRU and not into the atmosphere.
  • Maintain protection from overpressure or excessive vacuum.


  • The answer in the Series 4000 Marsh Hawk (TRV) Tank Relief Vent. The Marsh Hawk offers superior performance in normal and cold conditions with a bubble-tight standard Viton seal.
  • The Marsh Hawk also protects tanks from overpressure or excessive vacuum while maintaining tank access.
  • Bubble tight, repeatable sealing performance, even with tank hatch cover in open position.


  • The Marsh Hawk design is operationally more efficient eliminating flutter and maintaining low leak rates.
  • Our single spring adjustable pressure setting, guided release and seating adds to the bubble tight design.
  • A single gasket for both pressure and vacuum further decreases maintenance costs.

Although Marsh Hawk’s newer design includes a higher initial cost than traditional thief hatches, numerous long-term benefits far outweigh these initial costs.

  • Reduced maintenance cost with a single gasket for both pressure and vacuum
  • Lower priced OEM replacement gasket & lower priced OEM pressure and vacuum springs
  • Pressure spacers can be added and subtracted vs purchasing new spring for new settings
  • Mechanical design incorporates sealing mechanism into same position for repeatable performance
  • Accurate pressure settings with bubble-tight seal equals less time spent on site
  •  Reduced emissions and maintaining EPA flaring regulations
  • Consistent positive pressure allows NGL incompressible fluids to remain in liquid state

Cimarex Delaware Basin:

Marsh Hawk Series 4000 trial included (4) tanks, each replacing leaking Traditional Style Thief Hatches. Cimarex owned combustible gas detection camera shots indicate leakage rate between 0 and 20 scale from the Traditional Style Hatches. Best performing hatch leaked at an unimpressive “8” rate with the others being worse; note that the average of the (4) hatches was at an “11” leakage rate. The Traditional hatches were removed by Precision Valve Services (PVS) Technicians (Carlsbad NM), Marsh Hawk Series 4000 tank relief vents were installed. When tanks were placed back in active service, there was zero “0” leakage rate through day 4 of consecutive daily evaluation by Cimarex. Day 5 one Marsh Hawk unit registered a “1” leakage rate from the connection to the tank, increased torque at that location returned the leakage rate to “0” and the 7 day trial period was deemed a tremendous success. LDAR was nullified. The first 4 Marsh Hawk’s above continue to remain leak free since early June 2019.

Subsequent installation for Cimarex Delaware Basin:

On a separate Cimarex location 6 tanks were identified on a location where the VRU was largely ineffective. Traditional Style Hatches were removed and replaced by Marsh Hawk’s. Cimarex Facility Operator was on site witnessing the installation, when the Marsh Hawk internals were installed the VRU instantly came on. The VRU on location hadn’t operated in more than a month because of leaking Thief Hatches.

Sealed tanks = Increased Profits:

Higher ambient temperatures and unstable pressure containments allow for Natural Gas Liquid (NGL) incompressible fluids (light hydrocarbon “distillate” or “condensate”) to flash off from liquid to gaseous phase very easily. It is common for NGL storage tanks to lose 1 to 2 feet of liquids overnight in summer. The Marsh Hawk 4000 Series enables a more stable environment that forces the NGL to remain in liquid phase and enables collection and sale of these products more consistently. The increase in NGL recovery has the potential to pay for the initial hatch purchase over a weekend.

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