The re-engineering of existing valves is becoming increasingly more attractive, owing to their escalating cost, says valves manufacturer PSV Mitech senior design engineer Peter Connan.

He says PSV Mitech offers a valve retrofit service that fits new internals and top works to an original valve.

The company’s valve retrofit service is usually undertaken on site. Connan explains, however, that a valves system must first be removed from service and dismantled. In some rare cases, the valves may also need to be machined on site or at PSV Mitech’s workshop, in Elandsfontein, Johannesburg.

“We have modified many valves systems through our valve retrofit service, particularly large valves, including valves sent to us from the UK,” he highlights.

Connan says, in many cases, when an existing valve needs to be replaced at a plant, the valve body is still in good condi- tion, but the trim is no longer suitable, while the actuator and positioner also need upgrading.

“In these cases, PSV Mitech’s trims will be designed to suit the application and can be selected from an extensive range of components, which includes the energy- dissipating disk stack. Materials will be chosen to ensure a valve’s safe operation and long life,” he states.

Connan points out that the cost of retrofitting valves that are smaller than 150 mm or have a pressure rating below 600 bar is generally not justifiable.

However, he says retrofitting becomes progressively more worthwhile for larger- sized and higher-pressure-rated valves.

“With PSV Mitech’s local manufacturing knowledge and experience, customers can be confident of receiving quick service and, in many cases, receive a valve that will perform better than when originally supplied,” states Connan.

Two Large Valves Produced

In October, in a press release, PSV Mitech announced that it had manufactured two of its largest ever valves.

According to the company the two 600 mm globe control valves are being supplied to its UK-based agent Valve Solutions.

The valves are for use on a hydrocarbon gas application with an inlet pressure of 32 bar and an outlet pressure of 3 bar with a flow rate of 750 000 kg/h.

“The amount of energy that [the valve] needs to dissipate is a staggering 80 100 kW. The internal trim in the valve is a pressure balanced plug with a three-stage high-energy dissipating stack. The overall height of the valve and actuator is 4.1 m and each valve weighs 4 800 kg,” states PSV Mitech, adding that the valves were manufactured, assembled and tested in 12 weeks and all the parts making up the valve are 100% South African.

The body and bonnet material of the valves is ASTM A 216 WCB, while the plug and seat are made from 316 stainless steel with stellite grade 6 material on the seating surfaces. The high-energy dissipating stack is made of 316 stainless steel and the pressure balance seal is made of hydrogenated nitrile butadiene rubber, low temperature, rapid gas decompression resistant material.

PSV Mitech states that the special skids were designed as part of the valve so that the valves can easily be assembled and loaded into a container for transport. The skids will also be used in rigging the valves into their final position.

PSV Mitech also stocks hygienic, dosing control, bespoke, damper, sweep angle and plastic in-line globe control valves, besides others.