Manufacturers from China

Tuesday, May 3, 2016

EastMachinery Tell you Why Choose a Positive Displacement Pump

The decision to choose a positive displacement pump over a centrifugal is not always a clear one. They each have very different behaviors and if not familiar with them, it may be difficult to understand how a positive displacement pump could fit into your process.

Positive displacement pumps are a more efficient choice than centrifugal pumps in some situations. If any of the conditions or applications below are in your process, a positive displacement pump should probably be used.

1, HIGH VISCOSITY

Centrifugals have issues pumping viscous liquids, becoming very inefficient at even modest levels. Positive displacement pumps, on the other hand, have no problem moving thick liquids.

2, LOW FLOW

Oftentimes, a centrifugal pump is run off its BEP when a lower flow is desired, much to the pump's detriment. If you read our previous post "How To Read a Centrifugal Pump Curve", you'll recall that running a centrifugal off its BEP can cause excessive energy consumption, damage to the pump, and overall poor performance.

A positive displacement pump, however, is well suited for these conditions, providing constant flow of fluid at a given pump speed.If you're trying to get the pressure or flow you need by operating a centrifugal pump off its best efficiency point (BEP), a positive displacement pump may be a better choice.

3, METERING

Positive displacement pumps are an ideal choice for metering applications. They deliver constant flow, allowing them to easily meet process requirements. Some common types of positive displacement pumps used for metering are:

Peristaltic

Gear

Diaphragm

Plunger

Piston

4, HIGH PRESSURE REQUIREMENTS

Positive displacement pumps are excellent for applications that require high pressure, with some models producing over 1,000 psi (2,300 ft). Due to the positive displacement pump's design however, if kept in operation against a closed discharge valve, it will continue to build pressure until the line bursts, the pump is damaged, or both.

5, SHEAR SENSITIVE LIQUIDS

Centrifugal pumps generally operate at higher speeds when compared to positive displacement pumps. the higher speeds can shear liquids, making centrifugal pumps a poor choice for liquids like tomato paste and latex paint. Positive displacement pumps operating at lower speeds can be more gentle on products, and are usually preferred in these types of applications.

Centrifugal pumps and positive displacement pumps behave very differently. Understanding their behaviors can help you be sure to choose the right one for your application.

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Failed Mechanical Seal Puts Cold Storage Facility Hot On The Trail For Solution

A company specializing in temperature-controlled warehousing and logistics for the food industry recognized an issue concerning a failed mechanical seal on a Goulds 3196 ammonia pump. Being that ammonia pumps are critical to maintaining temperatures at a cold storage facility, identifying the problem and appropriate solution was dire. In conjunction with the facility's Maintenance department, the engineering and service teams at Crane Engineering worked tirelessly to troubleshoot and identify the right solution.

This cold storage facility has two primary pumps used to maintain temperature throughout the facility. One of these pumps experienced catastrophic seal failure less than one year after it was replaced by the customer. To make things worse, the other critical pump wasn't doing much better as it slowly leaked as well. The customer was in a tough situation as it was now June and the weather was really starting to heat up – making it even more difficult to maintain the cold temperatures. Time was running out.

Instead of simply installing a new seal, the team at Crane Engineering made the decision to troubleshoot and determine why the customer-installed seal failed in under one year. Oftentimes there is an underlying cause for seal failures, especially when they happen within a short period of time. It was determined that seal selection was not the issue, this style of seal is commonly used across the cold storage industry and is widely accepted due to its reliability.

THE SOLUTION

The pump was disassembled by Crane Engineering's service team in Kimberly, Wisconsin. The condition of critical parts was assessed to determine if replacing the seal would fix the problem. With a number of components showing significant wear, it was determined that replacing the seal would only be a temporary solution, as the worn components directly impact the overall reliability of the seal.

A Crane Engineering Account Manager also noticed the seal's piping plan wasn't ideal as it sloped in the wrong direction with tight 90 degree elbows instead of gentle slopes. A proper pipe installation method was discussed and necessary changes were made to ensure adequate lubrication.

THE RESULTS

The pump repair and installation took a total of two days. A number of causes for the shortened seal life were found, and necessary components on the pump were either repaired or replaced. Since then, the pump has operated flawlessly, and the facility came out with a greater depth of knowledge on the subject. Root cause analysis of the failed mechanical seal helped to ensure maintenance personnel could extend the life of their pumps minimizing costs associated with repeated mechanical seal failure.

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Friday, April 15, 2016

To be continued - A Few Simple Principles Guide You To The Best Seal Flush Plan

--- To be continued

3. External Flush

The external flush method is used when it's desirable to isolate the seal from the pumped fluid. However, if you do not have a suitable flushing liquid available or if diluting the pumped fluid with the flushing liquid is unacceptable, this is not an optimal solution. This method consists of a minimal flow of a clean, relatively cool liquid (usually water) from an external source injected into the seal gland flush connection at a pressure higher than the pump seal chamber pressure. The external flushing liquid flows past the seal and into the pump, mixing with the pumped fluid. Usually a flushing liquid pressure of about 10-15 psi above the pump seal chamber pressure is sufficient.

Flow rates of about 0.25-0.50 gpm are typical, but any positive flow is probably adequate unless there is a need for a specific flow rate to keep the seal temperature at a desired level. A restriction bushing or lip seal can be installed at the seal chamber throat to minimize the flush water flow. A control valve, gauge, and flow meter should be installed in the flushing liquid supply line to provide the control functions necessary to set and monitor the flushing liquid supply, with the flow meter being the most important so that a positive flow of flushing liquid into the pump can be confirmed.

An external flush can perform several functions:

Flushes damaging solids away from the seal

Isolates the seal from the pumped fluid

Cools the seal

Carries away seal generated heat

But, it also has its disadvantages:

Additional costs

Potential problems may occur when diluting the pumped fluid

Possibility of seal failure when the flushing liquid supply is interrupted by system failure or human error

4. Induced Closed Loop Circulation System

Not common, but may be recommended when it's necessary to control the temperature at the seal to a level different than the pumped fluid. It can only be used with a seal that has special circulating features. The seal must be equipped with a device that generates some circulation flow (basically a small impeller) and piping in and out of the seal chamber through a heat exchanger. In most cases a bypass flush with a heat exchanger would be the more reliable method to obtain the same results, but an induced closed loop circulation system can be used to reduce the heating/cooling load since only a small amount of liquid contained in the seal chamber is circulating through the heat exchanger.

If you are considering an induced closed loop circulation system contact your local seal supplier to come up with the best system design.

A Few Simple Principles Guide You To The Best Seal Flush Plan - EastMachinery

Are you Tired to watching your money spiral down the drain from mechanical seal repair or replacement? A few simple principles can guide you to the best seal flush plan for your installed mechanical seal, allowing the seal to operate in an environment that generates optimal seal life yet minimizes costs from water usage and product dilution. Today, we'll identify 4 flush piping plans for single mechanical seals and how they work. In future articles, we'll dive into double mechanical seals and packing, so stay tuned!

1. No Flush

Can only be used if the pumped fluid is clean, does not exceed the temperature limits of the seal, is compatible with the seal components, and is in no danger of vaporizing or solidifying when exposed to the additional friction heat generated by the seal. If this plan is used, a tapered or self-venting seal chamber is highly recommended.

2. Bypass Flush

This method is used when the pumped fluid is clean, does not exceed the temperature limits of the seal, and is compatible with the seal components. It's not recommended if the pumped fluid contains solids that could adversely affect the seal or if the temperature of the pumped fluid exceeds the maximum temperature for the seal.

Normally, this method consists of piping run from the pump discharge to the flush connection on the seal gland, providing flow from the pump, past the seal, and back into the pump through the seal chamber throat. It can also be piped from the flush connection on the seal gland back to the pump suction, which would result in the flow going the opposite direction and can have the added benefit of lowering the operating pressure at the seal. If warranted, accessories such as a heat exchanger or pressure reducing orifice can be installed in the piping.

A bypass flush provides circulation flow past the seal faces to carry away seal generated heat, so the seal operating temperature will stabilize at the temperature of the pumped fluid. This method is simple, reliable, and inexpensive. It does not result in product dilution and is the preferred seal flush method unless there is a specific reason not to use it.

--- To be continued

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EastMachinery Tell you Why Get Low Flow and Pressure From A High Pressure Pump?

Every facility manager knows that he or she could be held at least partially responsible for periods of reduced productivity and increased downtime. But what happens when a critical high pressure pump doesn't meet performance expectations? Leveraging the skills and expertise of the Crane Engineering team, one manufacturer solved this problem.

The Manufacturer's Challenge

A food manufacturing plant in southern Wisconsin specializing in the production and packaging of carrots, corn, mixed vegetables, peas, potatoes, and stew vegetables installed high pressure pumps to supply water to the plant for clean up after a long day of production. The main purpose of these pumps was to supply enough flow and pressure to hoses placed around the plant for cleaning and pressure washing work areas. After these pumps were installed, they still weren't seeing enough flow and pressure to all of the nozzles and hoses placed throughout the plant. This was a problem that needed to be addressed.

The company was running three (3) Roto-Jet high pressure pumps in parallel to supply flow and pressure to the plant. Many food manufacturing plants, including this one, use fixed flow orifices on the discharge of the pump to protect it from running off the curve and destroying the pump, which could be detrimental in terms of maintenance costs and unscheduled downtime for the company.

Why A Fixed Flow Orifice Is Not Appropriate

Using the fixed flow orifice on the discharge of the pump causes a significant amount of wasted energy and places limitations on the capacity and production of the pump.

In coordination with the facility's maintenance department, it was decided to provide a long-term, more substantial solution by removing the orifices and sticking with the standard size discharge. The team at Crane Engineering then sized, selected, and installed a pressure regulating valve in the discharge of the pump with a controller to regulate the valve. This allowed for full control of the high pressure pumps, while increasing flow rate and discharge pressure throughout the plant. Problem solved!

Benefits of the Pressure Regulator and Controller Setup

Using the pressure regulator and controller setup versus the flow orifice helped to increase productivity, and also ensured consistency across the board for higher flow rates and pressure for which the pump was initially designed.

Wednesday, April 13, 2016

How A Paper Mill Found the Right Mechanical Seal for A Pulper - EastMachinery

Is there anything tougher to seal than a bottom entering pulper? Rotors on these machines take a beating from market pulp bales and recycled material, causing large radial shaft deflections. Traditionally, seals have been packed, allowing for leakage, loss of product, wet floors, and thousands of dollars wasted on downtime and gearbox repair.
The maintenance department at New Page decided they weren't going to take it anymore. The leaking seal on "Slab Broke Pulper" was simply costing them too much. They determined that the seal they needed would have to be fast and easy to install, very low maintenance, and withstand the heavy shock and vibration that occurs during normal operating conditions.
New Page decided to install a John Crane fully split mechanical seal with compression ring rubber bellows. The rubber bellows would add flexibility and shaft deflection so angular misalignment and run outs were tolerated.
The mechanical seal they chose accepted:

Radial shaft movement of 0.125"
Shaft run out up to 0.020"
Stuffing box waviness up to 0.030"
Axial end play up to 0.060"
Out of squareness box face to the shaft of up to 0.100"
Temperatures up to 180° F
Pressures up to 80 psig
Speeds up to 1,800 rpm

The maintenance team at New Page placed bets on the number of days the mechanical seal would survive, confident the harsh operating conditions would cause it to leak.
But it never did.
Fast forward 21 years. The maintenance team is again looking at "Slab Broke Pulper" to investigate an issue concerning pulp break-up. They inspect the unit and find that the same John Crane seal installed in the early 90s remained, and still, no leaks.
Crane Engineering Account Manager Bob Linder, and Service Technician Dave Holtz, along with two of the mill's maintenance people, rebuilt the seal and promptly put it back into service on "Slab Broke Pulper". Two years later, and despite a bent shaft, the mechanical seal continues to perform against leakage, saving the mill thousands in rebuilt gearboxes and time spent re-packing stuffing boxes.

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5 Things You Must Know for Sizing a Pressure Regulator, Correctly!

A pressure reducing regulator is commonly used to manually control pressure of a liquid, gas or steam. Choosing the right regulator for your application can be challenging. There are 5 variables required to size any pressure regulator and properly calculate Cv: upstream pressure, downstream pressure, flow range, temperature and fluid type. We define each variable and talk about why it's crucial to sizing a pressure regulator.

Please note: Cv is a coefficient of flow for valve sizing. It's used to quantify valve flow performance and can vary with both size and style of the valve or regulator. Once you calculate the required Cv range, you'll know the valve or regulator is sized correctly to handle the actual flow.

1. UPSTREAM PRESSURE

Supply pressure or Inlet pressure. This is the pressure upstream of the regulator. This pressure could be coming off of a main header at 100 psi. If it is a higher pressure, such as 1,000 psi, and your goal is to regulate a much lower pressure, less than 100 psi, then a second regulator may be required to knock down the pressure in two stages: one high pressure regulator and one low pressure regulator.

2. DOWNSTREAM PRESSURE

Outlet or Control Pressure set point or range. This is the pressure downstream of the pressure reducing regulator. The pressure levels are what you are attempting to control. It could be a specific pressure point, like 30 psi, or a range of 5 to 20 psi. The difference between upstream and downstream pressure is called a "pressure drop" or "pressure differential".

3. FLOW RANGE (minimum, maximum and normal)

It's a good idea to size the regulator at a minimum of 3 separate points in order to get a range of flow requirement. This gives you a safety factor, so the regulator is not over or under-sized.

4. TEMPERATURE (minimum and maximum)

Temperature can affect the required Cv. Note that temperature does not affect Cv nearly as much as pressure and flow.

5. FLUID TYPE

Determine what fluid is going through the regulator. Is it liquid, gas or steam? What are its properties? Understand that sizing formulas are different for each type of fluid. For example, the formula for critical pressure drop is different than non-critical pressure drop for gases. For steam, you must know whether it's saturated steam or super heated (higher temperature).