Hells HTD-37 Thermodynamic Steam Trap


Thermodynamic steam traps have a unique operating principle which relies on the dynamics of water and flash steam. They are simple, robust and reliable and can operate up to very high temperatures and pressures. Their construction, use and benefits are detailed on this page.

The thermodynamic trap is an extremely robust steam trap with a simple mode of operation. The trap operates by means of the dynamic effect of flash steam as it passes through the trap, as depicted in the image below. The only moving part is the disc above the flat face inside the control chamber or cap.

On start-up, incoming pressure raises the disc, and cool condensate plus air is immediately discharged from the inner ring, under the disc, and out through three peripheral outlets (i).

Hot condensate flowing through the inlet passage into the chamber under the disc drops in pressure and releases flash steam moving at high velocity. This high velocity creates a low pressure area under the disc, drawing it towards its seat (ii).

Body material is forged steel and inner parts are stainless steel. Seat and disk material is hardened. Operating surfaces precision machined for perfect leak proofing and HTD 37 has an inner filter that can be maintained very easily. The spare part also available.

At the same time, the flash steam pressure builds up inside the chamber above the disc, forcing it down against the incoming condensate until it seats on the inner and outer rings. At this point, the flash steam is trapped in the upper chamber, and the pressure above the disc equals the pressure being applied to the underside of the disc from the inner ring. However, the top of the disc is subject to a greater force than the underside, as it has a greater surface area.

Eventually the trapped pressure in the upper chamber falls as the flash steam condenses. The disc is raised by the now higher condensate pressure and the cycle repeats (iv).

Connection Types

  • 1/2″-3/4″-1″ screwed BSP or NTP
  • 1/2″-3/4″-1″ Socket weld ANSI B16.11
  • DN15, DN20, DN25, EN 1092-1 Flanged
Hels Steam Trap HTD-37 Thermodynamic
Hels Steam Trap HTD-37 Thermodynamic


  • Iron Machines
  • Drying Unit
  • Pressing Unit
  • Steam Jacket Pipelines

Working Conditions

Max. Working Pressure PMO  40 Bar
Max. Working Temperature TMO 400 °C
Max. Differential Pressure ΔPMO 32 Bar


Body C22.8 (ASTM A105)
Kapak Carbon Steel
Filter Stainless Steel/ AISI 304
Disc Stainless Steel/ AISI 420
Seat Stainless Steel/ AISI 420

Certification: EN 10204 3.1

Advantages of the thermodynamic steam traps

  • Thermodynamic traps can operate across their entire working range without any adjustment or change of internals.
  • They are compact, simple, lightweight and have a large condensate capacity for their size.
  • Thermodynamic traps can be used on high pressure and superheated steam and are not affected by waterhammer or vibration. The all stainless steel construction offers a high degree of resistance to corrosive condensate.
  • Thermodynamic traps are not damaged by freezing and are unlikely to freeze if installed with the disc in a vertical plane and discharging freely to atmosphere. However, operation in this position may result in wear of the disc edge.
  • As the disc is the only moving part, maintenance can easily be carried out without removing the trap from the line.
  • The audible ‘click’ which occurs as the trap opens and closes makes trap testing very straight forward.