Stainless steel pulsation damper, whole and in section

pulsmin pulsation dampersThe dryer switches over. The compressor stays calm.

Stainless steel pulsation dampers for compressed air production in rail vehicles. No power, no maintenance, since 2001.

The dryer switches over roughly every 50 seconds to several minutes.

Adsorption dryers regenerate in cycles. When switching over they briefly draw a large amount of compressed air, and at every compressor stop the line between compressor and dryer outlet is vented to atmosphere. Both times the pressure drops abruptly. The pressure sink travels back to the compressor at the speed of sound and expands the compressed air there explosively across the filter element of the oil separator.

Oil in the compressed air networkResidual oil content rises. Pipes, dryer and components are contaminated.
Ruptured oil mist separatorsThe alternating pressure differences wear down the filter fleece until it tears.
Dust and valve damageWith piston compressors, the discharge pulsation adds to this: dryer granulate breaks down into dust in pipes and components, and reed valves are damaged.

Installation point with an adsorption dryer, per instruction manual: between compressor and dryer, ideally directly in the compressed air inlet of the dryer. All parts upstream are then protected against the dryer switching. With membrane dryers the damper sits downstream of the dryer, in any case upstream of the relief valve.

Normal operation

Open while everything is calm.

The compression spring holds the piston off its seat. Air flows through the piston and past the seat; the flow loss is negligible.

The dryer switches over

Pressure drops downstream of the valve. The piston closes.

The air still being delivered can only pass through the bypass bore in the piston. It is sized so that operating pressure is held upstream of the valve.

Pressure equalised

Equal pressure on both sides. The valve opens.

Compressor, oil separator and the pipe upstream keep working in quasi-steady-state operation. No power, no controls, no adjustment.

Without PDV

Every time the dryer switches, the pressure collapses.

The line is relieved abruptly. Afterwards the compressor has to refill the entire line including the dryer.

With PDV

With the PDV only a small dip remains.

The valve closes as soon as the pressure behind it drops. At the compressor only an insignificant pressure drop remains; only the dryer has to be refilled.

Pressure after the compressor · schematic

Schematic, after diagram 2 in the article in “Verkehr und Technik” 2016, issues 9 and 10, not to scale. Article (PDF, German)

No cable. No electronics. Just mechanics.

Six parts. All stainless steel.

Housing, piston and spring in stainless steel 1.4301. No soft seals, nothing that can embrittle.

Parts list PDV-DS

Hover over a part to see it on its own.

Measurement report Rev. 02 · 19 January 2018

Measured on a piston compressor.

Kötter Consulting Engineers measured the effect of a PDV-DS on an oil-free piston compressor in a shunting locomotive. The pressures in the pipe upstream and downstream of the valve were recorded simultaneously.

Compressor: reciprocating piston, oil-free, two-stage
Intake volume flow: 2,150 l/min at 1,579 min⁻¹ (as stated by the compressor manufacturer)
Gauge pressure upstream of the PDV-DS: 10 bar
Valve: PDV-DS G 1"
Sampling rate: 2,000 Hz
Measured by: Kötter Consulting Engineers GmbH, Rheine

Pressure over time at measuring points P1, P2 and P3 at 10 bar gauge upstream of the PDV-DS. Redrawn from fig. 3 of the measurement report.

Pulsation upstream of the PDV-DS (P1): 0.604barpeak to trough
Residual pulsation downstream of the PDV-DS (P2): 0.254barAccording to the dryer manufacturer, less than 0.5 bar is sufficient to keep the desiccant grains from moving against each other, abrading and turning to dust.
Measured damping: 40.3%excluding the share of the piping components in between, at 155 mbar pressure loss
Pulsation frequency: 26.3Hzat 1,579 min⁻¹

Damping rate of the PDV-DS as a function of the pressure loss (fig. 4). More damping costs pressure loss, for example about 60 % at around 280 mbar.

“Not as good as possible, but as good as necessary!”

Summary on sizing the PDV-DS in the measurement report · Measurement report (PDF, German)

Install and forget.

The valve is maintenance-free. It needs no adjustment: pulsmin builds it to your volume flow and the required holding pressure.

PDV for screw and rotary vane compressors PDV-DS for piston compressors Instruction manual, schematics and press

Data sheet per instruction manual rev. 06 and pulsmin data
Medium and ambient temperature	−60 to +140°C
Permissible operating pressure (gauge)	20bar
Intake volume flow	up to 4,000l/minNominal sizes G ½" (M 22×1.5), G 1" and G 1¼"
Pressure drop upstream when closing	max. 1 to 3barTest value for the function check after installation
Material of all parts	Stainless steel 1.4301
Proven in service down to	−50°CCompressed air systems for Russia
Mounting position	anyhorizontal to vertical, observe the flow direction
On the market since	2001

In service.

pulsmin pulsation dampers sit in the compressed air systems of rail vehicles, metros, mountain railways and buses. A selection, with photos of the vehicles and installation points.