MART Response to Proceco Regarding Pump Performance

Following is a Report written by Robert Burns, P.Eng for Proceco that critiques the MART Pump Technology article in which the Proceco engineer attempts to refute statements made by MART engineers. The Proceco Report is not only in error as regards MART Pump Systems, but also conflicts with the Laws of Physics.

This article is in response to the Proceco Report. For ease of reading, MART has inserted its comments in the text of the Proceco Report in Blue Bold.

The Proceco Document follows:

A Proceco Technical Analysis: MART’s Pump Technology Demystified

May 14, 2007

It is not the intent of this analysis to speak negatively of our competition but rather to
provide our sales people with the facts regarding Mart’s pump technology, which Mart
often claims to be superior to Proceco’s. Proceco started designing and building their own
high-pressure pumps (over 70 psi) in the mid-eighties, when they could not source pumps
that operated reliably under the harsh conditions of power spray washing.

Our competition would have you believe that they not only invented spray washing, but
also invented pump technology! Unfortunately, they often get away with this because,
most of us in our busy everyday lives do not have the time or information to challenge
their claims. Fortunately, facts speak for themselves and the information below will help to
demystify their claims.

Who does the engineering?

Mart claims they have engineered their pump systems. However, the truth is that they use
standard pumps manufactured by the Carver Pump Company. These are catalogue items
available to the general industry.

In fact, Mart’s entire pump line-up from 20 to 90 HP is made up of either a single pump model with varying impeller diameters or a combination of two pumps, again with varying impeller diameters.

This is illustrated with several examples:

1. Mart 20HP pump, rated at 269 USGPM at 107 psi (247 ft). Mart uses a vertical cantilevered pump, with 3"×2½"×10" wet end*. The power curve for this pump with an 8" diameter impeller corresponds to the above ratings (provided the motor operates beyond its normal service factor. (More on this later in this document).

2. Mart 55HP pump, rated at 356 USGPM at 187 psi (432 ft).
Mart uses two pumps in a series arrangement. The primary pump is a vertical cantilevered model, with 3"×4"×13" wet end, and the secondary pump is a 3"×2½"×10" wet end. The combined curves for this pump arrangement achieve a total of 55HP (25HP + 30HP) with the above ratings.

3. Mart 70HP pump, rated at 371 USGPM at 203 psi (469 ft)
This is the same model combination as above but with different impeller sizes producing 70HP (20HP + 50HP) with the above ratings.

The truth about efficiency

Another claim made by Mart is the efficiency of their pumps. There are different ways to
interpret efficiency. Let’s take for example, the following horsepower formula, published
on Mart’s web site at http://www.martwash.com/html/seminars_articles/pumptech.htm.

EFF = GPM × Head × Specific Gravity
Horsepower × 3960

Mart claims that their 20 HP pump described above is 88.3% efficient. Sounds a bit exaggerated to me, so let’s see if this is right! By applying the pump rating provided by Mart to the formula above:

EFF = 269gpm × 247’ × 1.0
20HP × 3960
EFF = 83.8% (there appears to be a typo on Mart’s website)

After further analysis of what appears to be an extremely efficient centrifugal pump, it
becomes clear from the horsepower curve for the model in question (not shown) that
25HP is actually required at 269gpm (247' head). One can get 25HP from a 20HP motor by operating it at 25% above its nominal rating (1.25 service factor). If this were the case (which in most cases is not good practice) the above formula would yield an efficiency of 66.7%. Incidentally, this is what the Carver Pump Company publishes as the efficiency of this pump model at that flow rate (see curve below).

That is a more than a 20% gap in efficiency!

The Proceco efficiency calculation is wrong. MART Pump Performance data are accurately taken and recorded by MART at the nozzle tips of each Power Washer prior to shipment. MART 70 Duplex Pump efficiency is 83.8%, measured at the nozzle tips.
 
The Proceco performance data do not apply because their engineer reports the wrong pump configuration. Further, the Proceco engineer does not understand the benefits of the MART Duplex (turbo) Pump System over their simplex pump.

As already covered in detail, the Duplex MART Pump System does not run in tandem, but in series. The MART Low Speed, High Flow 15 HP Suction Pump feeds the suction side of the High Speed, High Pressure 40 HP Wash Pump. The MART Suction Pump maximizes flow at its lowest pressure and, because solution is being force fed by the Suction Pump, the High Pressure Wash Pump maximizes pressure without any suction losses.

By contrast, the Proceco single stage pump must provide solution flow AND pressure. Operating pressure is always highest at the lowest flow rate, and lowest at the higher flow rate. Therefore, the Proceco engineer must determine “the sweet spot” of the pump, which is a compromise between highest flow and highest pressure. The Proceco engineer will select operating parameters that sacrifice pressure for flow, or vice versa, but he cannot maximize both pressure and flow. This constraint does not apply to the MART Duplex because each Pump has only one function – flow or pressure.

For the record, single-stage centrifugal pumps usually have less than 70% efficiency
when operated at the low-flow and high-pressure conditions in question. True
To further elaborate the point, the graph below shows that such a pump with a specific
speed (a dimensionless parameter used in pump engineering) of less than 1000 is not
capable of achieving efficiencies greater than 68% at that given flow rate (269 gpm).
Specific Speed (Ns) = RPM * GPM1/2
Head (FT) ¾
(Ns) = 3500 * 2691/2
2473/4
(Ns) = 921

Ref: Centrifugal Pumps, Design and Application 2nd Edition, Val S. Lobanoff, Robert R. Ross

Our competition also claims that “Duplex and Quadroplex Pump Systems operate at the
highest efficiency”. In fact, the overall efficiency of these centrifugal pumps in series
(duplex) can never increase.

These claims and statements by Proceco are not true. The MART Suction Pump, operating at its low design pressure, draws in the maximum possible solution flow. The Suction Pump force feeds its discharge into the suction of the High Speed Wash Pump so that its only efficiency losses are caused by friction. Thus the full energy of the High Speed Pump is geared towards producing pressure. The discharge pressure at the nozzle tips is the combined pressure of both Pumps. Among the many significant advantages of the MART dual stage Pump System is that it can pump extremely hot solution without flashing, pulsating or cavitating, and without creating foam from pump-related causes. This performance is not possible with the Proceco simplex pump. (Note in the Proceco comments above the graph regarding specific speed that there is a 2 point penalty – 2 pts out of 66 is 3% - that results because the Proceco has an open style impeller pump while the MART impeller is closed style)

The overall efficiency of a series arrangement is simply the combined output over input of the individual pumps; assuming of course both efficiency points were taken at the same flow rate. To demonstrate this in an example, the Mart 55HP Duplex pump will be used: Mart duplex 55HP; rated at 356 gpm / 187 psi (432 ft) uses 2 pumps in series (Pump1 + Pump2) Pump1: 25HP; rated at 356 gpm @ 175 ft; (Efficiency rated at 63%) Pump2: 30HP; rated at 356 gpm @ 257 ft; (Efficiency rated at 73%) Note: The final pressure and horsepower of pumps combined in series is simply the sum of both pressures and horsepowers respectively. Therefore, the efficiency of the pumps combined:

EFF = 356gpm x (175+257)’ x 1.0
(25+30) HP x 3960
EFF = 70%

The MART responses are based on solid engineering and the Laws of Physics. Throughout this reply MART has shown why none of the Proceco data and statements in this Report is accurate. Because the premises of their engineer are in error, so are the conclusions.

Conclusion

As you can see, if information goes unchallenged, it can lead to improper decisionmaking.

Thank-you,
Robert Burns, P.Eng
Proceco Ltd.
www.proceco.com