Liquid Dynamics International Ltd. - Piping System Analysis / Piping System Simulation

LDi – P30

These examples of LDi PulseView output are from a version compiled for a deep sub sea methanol injection system, 6.25 miles (10 kilometers) to the well-head. Flow was generated by a multi-layer diaphragm head pump, against a total system resistance at the pump, of 700 Bar.

To read each set of plot lines, relate each to "Recip-View" piston position.

"Suck. Pres. View"
Suction damper too far, pressure response of supply pipe system
Dynamic “dt” pressure pulsation analysis seconds from start

Saving the cost of building a system which malfunctions, by generating an LDi PulseView model first, is only practical, when the necessary investment is made, to collect accurate input data.

"Suction Valve-View" destabilized valves)
Suction check valve response
Dynamic “dt” valve analysis, time since pump start in seconds
Note: Delayed suction check valve opening due to decompression of large dead volume in cylinder. Overshoot, rebound from short valve stop. Failure to reseat at end of suction filling stroke.

A. See "Suc-Pres-View", For enough pressure decay to allow the suction check valve to open.
B. See "Recip-View", When Suction Valve should open.

*Any or all of 3 things may be happening:
1. The liquid mass between damper and suction is too long. Slugs are going into oscillation and driving the checks off their seats.
2. Membrane response characteristics of suction damper may be unsuitable for this frequency.
3. Discharge checks may have some overlapping activity, and be exciting suction acoustics.

Small diameter stiff on suction diaphragm response to pressure pulsation
Dynamic “dt” diaphragm movement analysis seconds from start
Note in zoom area – evidence of discharge valve bounce feeding back to suction at beginning of suction cycle

The typed notations of on the plots are added to assist in understanding how a pump is affected by all the system parameters.

The response characteristics of diaphragm membranes are generated when attempting to stabilize pump & system.

Discharge damper, membrane resonance to pressure change
Dynamic “dt” membrane analysis seconds from start
Note in zoom area evidence of stored volume decompression from pump cylinder volumetric inefficiency.

In a system with a reciprocating pump, the root cause of the great majority of problems, begin with suction check valve response opening and closing delay. This is always found to be caused by the compressibility, SG, & cP of the system liquid, and the pipe design coming to the pump. The most common problem is too much suction force. Next are oversized suction pipes, and frequently, interaction / interconnection between pumps or between individual check valve pockets.

Stroke less than 0.25 seat diameter, discharge check valve response
Dynamic “dt” check valve movement analysis
Note valve flies open late, crashes end stop bounces closed again, chops volume flow, and bounces at end of cycle.

Pumps make flow, systems make pressure. The inertias in mass transfer are the essential components that require analysis. When the mass dynamics are established, then we examine "acoustic" response - know action, before reaction.

Understanding the effect of pipe design on pump performance will keep systems out of trouble.