Technical Products and Services Inc. Technical Products and Services Inc.
Your Single Source of Fluid Handling Products Since 1981

145 State Highway 94, Blairstown, NJ 07825  p.908.362.9981   fax.908.362.5631
 

TANK AND VESSEL WASHING SPRAY NOZZLES

 

With the broad selection of tank cleaning devices available today, the thought of manually cleaning a tank, mixer, duct or any other vessel that has been used to hold or convey a liquid or dry product should be a thing of the past.  Unfortunately, reports surface too often of injuries and even asphyxiation deaths from workers entering tanks for cleaning. What makes these especially disturbing is the fact that commonly available, inexpensive products are available that make these situations preventable.

Automated tank washing processes can be adapted to virtually any equipment configuration, large or small, simple or complex, easy or difficult. With at least a dozen manufacturers of such devices, there is no shortage of equipment choices. The most difficult question in many situations is simply, "What will work best for my application?" For purposes of this presentation, we will limit our scope to evaluating the individual tank washing devices, both static and rotating, as are commonly available from a large group of manufacturers, and how they are used. Full CIP systems and how they are configured are beyond what we can cover in this type of venue. We will consider various types of cleaning situations, requirements of different tank sizes and configurations and the spectrum of tank washers available. (Also for purposes of this presentation, the word "nozzle" means a device to spray, not a port or opening on a tank. I will use the term "spud" for the latter.)Let's begin the process by describing cleaning functions in a way that we can use throughout the discussion. For convenience's sake, here are three "classes" of cleaning which present different challenges. The term "soil" describes any material that we want to clean from the affected surfaces.

Class I

Here the soil is simply a liquid residue or light powder that does not adhere aggressively to the surface. Cleaning is simply a matter of rinsing the surfaces with a solution that washes away the soil and possibly disinfects the interior. Spray impact does not contribute significantly to the process. An example of this would be a tank used to hold milk.

Class II

A slightly more difficult situation where the soil does not rinse away so easily, yet it can be dissolved by the cleaning liquid. Spray impact helps move the process along but over time and with enough liquid, the surfaces will ultimately come clean. An example of this would be a tank that held molasses or white glue. It doesn't wash off easily, but water will soften it and wash it away.

Class III

The most difficult situation where the soil does not dissolve in the cleaning liquid. The process depends on the impact of the spray and washing action of the liquid to breakup and carry the soil away. An example of this would be a tank that held a powder that does not dissolve in water. Any caking on the walls needs to be blasted off and washed away with enough force to keep the soil moving.Of course, there are infinite variations and shades between these three designations based on the application. None the less, these should help as you evaluate your own specific needs. The sizes and configurations of tank washers make them particularly suited to cover specific portions of the spectrum. Choosing an inadequate design will cause obvious problems, but making a choice that is overkill can be costly in purchase price and ongoing liquid consumption.

Major Design Groups

While there are dozens of tank washer designs from various manufacturers, for the most part they can be separated into three general classifications:

1. Static-Single or cluster nozzles designed to cover large areas without rotating.
2. Free spinning reaction heads-Rotating heads powered by the reaction force of tangentially directed sprays.
3. Mechanically driven-Units driven by liquid pressure or external power using gear drives for controlled pattern rotation.

There are a variety of designs within each class, each with its own advantages and drawbacks. No single design is appropriate for every application. Advantages balance downsides and there are performance tradeoffs at every turn. Your best position is to understand each of these and make the effective choice for your specific needs.

Here are the primary considerations for the major design classes. There are certainly exceptions to every generalization, but this information applies in the widest range of cases.

Static Tank Washers
The simplest and generally least expensive tank washers are nozzle heads that do not rotate, but provide wide coverage through the use of a cluster of individual orifices or slots. They come in a variety of sizes and shapes, but like most designs, they can be grouped into sub-classifications.

Spray Balls
These use a hollow shell, shaped like a ball or small pumpkin, with a large group of small holes that form many small solid stream sprays when the head is pressurized. In some cases there can be slots around the "equator" that send out a fan of spray in combination with the small holes. 

Best Applications
Class I and possibly light Class II cleaning with smaller tanks, usually smaller than 10' in diameter. The design adapts well to specialized and directional coverage requirements given their ability to concentrate spray wherever it's needed. They can mount in any position since they have no rotating parts.

Drawbacks


Cluster Full Cones
Here a group of full cone nozzles are mounted on a central hub, which acts as a common liquid supply. The sprays overlap so there is a cloud of droplets, which provides very complete coverage. Flow rates range from less than 10 gpm up to several hundred gpm, so the size range is huge.

Best Applications

Class I and possibly light Class II cleaning with smaller tanks, usually smaller than 8-10' in diameter. In most cases the smaller the tank, the better, as impact falls off very quickly as the spray travels from the orifice. With larger tanks, the impact is minimal, but the coverage is very complete. If the application demands a gentle spray, this would be the first choice.

Drawbacks

When making a selection, there are a number of considerations that apply to the whole variety. In general, the main points are as follows:

Best Applications
All classes of cleaning, especially I and II. Class III is also certainly possible if the impact requirement is not huge.

Free Spinning Reaction Heads
This segment of the spectrum is the largest and most varied. Reaction powered rotating tank washers are available from at least a dozen manufacturers. They can range from tiny heads less than I" in diameter to huge units spraying hundreds of gallons per minute.

Given the variety of designs, free spinning heads can handle everything from a bucket to a tank 30' to 40' in diameter. However, spray impact falls off quickly as distance increases.

Drawbacks


When looking at a specific design and matching it to an application, think through the particular features with the following points as your guide:

Flow Rate
It is difficult to give universal guidelines for how much liquid it takes to wash a tank since conditions vary so widely Suggestions range from .2 to .5 gallons per minute per square foot of internal tank surface. If there are few obstructions so the spray can propagate easily, and the tank is not too large, the lower end is probably adequate. For more difficult installations or aggressive soil, a higher flow rate may be required. Higher flow units normally produce larger droplets, which carry over greater distances and hit with more impact.

Spray Distance


Material of Construction

In this product category, almost all designs are either made from stainless steel or plastic, primarily PTFE (Teflon using DuPont's name) but a few others like PVDF and polypropylene are also available.


All-stainless steel units are very durable and can be subjected to extreme temperature ranges. The main drawback is ensuring that you have an appropriate grade of stainless if your environment is particularly corrosive. Units in exotic materials are normally very expensive.


All-plastic units are getting to be more common. They are normally inexpensive, especially those made from injection molded PVDF. All-PTFE units are an excellent choice for the most corrosive applications. While inexpensive, they are disposable since they cannot be reconditioned.


Stainless steel with plastic bearing inserts are a good compromise. They can be disassembled easily and the inexpensive plastic inserts replaced as they wear.


Nozzle Design
Tank washers have an amazing variety of nozzle and orifice designs: