Edwards Diffstak 63/150

Need help?

Do you have a question about the Edwards Diffstak 63/150 and is the answer not in the manual?

Overview

Function Description
Important Technical Specifications
Technical Data (Summary for M-model and P-model pumps)
Usage Features
Maintenance Features
Storage and Disposal
Service, Spares and Accessories

The Edwards Diffstak Mk2 Diffusion Pump is a high-performance, compact diffusion pump designed for use in applications where exceptional clean pumping without the use of extra traps or baffles, or the need for liquid nitrogen cooling, is required. It is available in various sizes, including 63/150, 100/300, 160/700, and 250/2000 models, with M-, P-, C-, and F-type configurations.

Function Description

The Diffstak is a three-stage fully fractionating diffusion pump with an ejector-type third stage. The pump body is water-cooled and made of stainless steel with a mild-steel nickel-plated base. The inlet-flange has an integral roughing pipeline into which a combined backing/roughing-valve can be connected in the Diffstak 63/150, 100/300 and 160/700 pumps. The Diffstak 250/2000 is designed to use separate roughing and backing pipeline valves. You may fit a vacuum gauge head to the roughing pipeline and to the backing pipeline. Heated within the inlet-flange is the low-impedance high-vacuum isolation butterfly-valve. Sectional views of the Diffstak pumps are shown in Figures 1 to 4.

Located below the valve is a baffle which consists of a water-cooled flanged cylinder with a detachable cover. The baffle also retains the jet assembly by spring pressure (except in the 250/2000 pump in which the interior is retained by a tie-rod). The interior jet system consists of a first, second and third-stage jet assembly with fractionating tubes. Above the jet system is a detachable first-stage jet-cap. The jet system is clamped together by a central tie-rod. The boiler is located in the base of the pump. The pump fluid is heated and vaporised by plate-type electric heater(s) (one or two, this depends on the size of the Diffstak). The heater has a fluid thermal cut-out and a drain-plug. The electrical supply cables from the heater are brought out to a terminal-box at the bottom of the pump for ease of connection to your electrical supply.

Pump fluid is heated in the boiler to produce a vapour which passes up through the interior of the jet assembly and emerges from the jets at high velocity vapour streams. The vapour streams condense on the cooled pump-body wall and drain into the boiler at the bottom of the pump for recirculation. A portion of system gas which arrives at the Diffstak pump-inlet is trapped in the vapour stream from the first-stage jet. The gases are compressed and transferred to the next stage. This process is repeated through the pump jet stages until the gases are removed by the backing pump through the cooled backing condenser. The guard-ring above the top-jet is designed to minimise any back streaming of pump fluid vapour. The guard-ring traps the fluid vapour and the vapour condenses on the cooled surface of the guard-ring. The fractionating feature of the Diffstak design provides a means of purging the fluid charge of undesirable light fractions and foreign matter and the process helps significantly towards the attainment of a low ultimate vacuum. The ejector jet also purges the fluid of any contaminants as it returns to the boiler and at the same time ensures a high critical backing pressure even when you use low vapour pressure fluids.

Important Technical Specifications

The Diffstak Mk2 Diffusion Pumps are available in four sizes: 63 mm, 100 mm, 160 mm or 250 mm diameter inlet-flange. The largest pump has a pumping speed of up to 2000 l s⁻¹. All four sizes of pump are available with unvalved collars and without the integral roughing connection, for use in applications where high-ultimate vacuum is of prime importance, or for pumping systems where a high-vacuum isolation-valve is not required.

Two unvalved versions are also available, for use in applications where the highest ultimate vacuum is required. These unvalved versions have 6 or 8 inch diameter flanges for use with copper compression gaskets. This provides simple, reliable, metal-to-metal sealing and is ideally suited to ultra-high applications. An ultimate vacuum of less than 2 x 10⁻¹⁰ mbar (2 x 10⁻⁸ Pa) can be achieved with a low temperature trap.

The basic models are as follows:

M-model pumps have a manually-operated high-vacuum isolation-valve.
P-model pumps have a pneumatically-actuated high-vacuum isolation-valve.
C-model pumps have an unvalved collar suitable for use with a bolted rotatable flange.
F-model pumps are unvalved and have a copper compression gasket (ConFlat) flange.

Cryo-cooled Diffstak pumps are also available in the same four sizes as the valved and unvalved pumps. These cryo-cooled pumps have a high conductance, liquid nitrogen cooled disc located above the water-cooled baffle. The pumps are designed for use in applications which require minimum pump down times when heavy vapour loads are pumped.

Technical Data (Summary for M-model and P-model pumps)

Specification	63/150M & P	100/300M & P	160/700M & P	250/2000M & P
Pumping speed (nitrogen)	135 l s⁻¹	280 l s⁻¹	700 l s⁻¹	2000 l s⁻¹
Pumping speed (hydrogen)	200 l s⁻¹	500 l s⁻¹	1300 l s⁻¹	3000 l s⁻¹
Minimum backing pump displacement for maximum throughput	5 m³ h⁻¹	5 m³ h⁻¹	12 m³ h⁻¹	40 m³ h⁻¹
Recommended backing pump	RV3 or RV5	RV5 or RV8	RV12 or EZM18	EZM40
Maximum pump pressure	1300 mbar	1300 mbar	1300 mbar	1300 mbar
Recommended pump fluid	Santovac 5	Santovac 5	Santovac 5	Santovac 5
Fluid charge (dry)	60 ml	125 ml	125 ml	500 ml
Inlet connection, compatible with	ISO63	ISO100	ISO160	ISO250
Backing connection	NW10	NW25	NW25	NW40
Cooling water connection	6 mm compression couplings	6 mm compression couplings	10 mm compression couplings	10 mm compression couplings
Minimum cooling-water flow at 20 °C	42 l h⁻¹	60 l h⁻¹	115 l h⁻¹	180 l h⁻¹
Heater power	0.45 kW	0.65 kW	1.35 kW	2.25 kW
Mass (M-model)	8 kg	12 kg	26 kg	59 kg
Mass (P-model)	9 kg	13 kg	27 kg	60 kg
Maximum voltage	48 V a.c.	48 V a.c.	48 V a.c.	48 V a.c.
Maximum current	380 mA	380 mA	5 A	5 A
Enclosure protection	IP67	IP67	IP22	IP22
Mounting screw torque	0.4 Nm	0.4 Nm	-	-

Usage Features

Installation: The manual provides detailed instructions for unpacking, inspecting, and connecting the pump to the vacuum system. It covers backing and roughing connections, cooling-water connections, and electrical connections. Specific figures illustrate the various inlet connections (M- and P-model, F-model, C-model) and installation details for different Diffstak models.
Pump Start-up: The start-up procedure involves closing the high-vacuum isolation-valve, selecting 'Backing' on the combined backing/roughing-valve, switching on the rotary backing pump, and waiting for the backing pressure to reach 0.5 mbar (5 x 10¹ Pa) or lower before switching on the electrical supply to the Diffstak.
Pump Shut-down: The shut-down procedure involves closing the high-vacuum isolation-valve, allowing the pump to cool, and re-evacuating the pump fluid.
Fluid Filling: The manual specifies the best fluid for each application and provides a filling procedure, including checking the drain-plug, pouring the required amount of fluid, and refitting the dipstick and 'O' ring.
Safety: The manual highlights important safety information with WARNING and CAUTION instructions. Warnings indicate potential injury or death, while cautions indicate potential equipment damage. Specific warnings include risks associated with cooling-water supply failure, hot surfaces, electric shock, and hazardous materials.

Maintenance Features

The manual outlines a comprehensive maintenance plan with recommended frequencies for various operations:

Check the pump fluid-level: 3 Monthly (heavy duty) / 6 Monthly (light duty)
Clean the cooling-coil: Yearly
Inspect the pump fluid (drain if necessary): As required
Clean the pump: As required
Clean the radiation shield: As required
Lubricate/inspect the high-vacuum isolation-valve: As required
Renew a heater: As required
Check the heater securing nuts: As required
Adjust or replace the position indicators: As required

Specific maintenance procedures include:

Check the pump fluid-level: Involves checking the fluid level in the boiler, removing the dipstick, and adding fluid if necessary.
Inspect the pump fluid (and drain if necessary): Details how to check for discoloured or charred fluid and drain/refill if needed.
Inspect and clean the pump: Provides instructions for inspecting the pump interior, cleaning with acetone, and ensuring all sealing-faces are scratch-free.
Remove the high-vacuum isolation-valve (M-model pumps): Steps to open the valve fully and remove the valve-plate.
Remove the high-vacuum isolation-valve (P-model pumps): Instructions for opening the valve pneumatically, removing the actuator, and dismantling the valve-shaft.
Dismantle the pump: Steps to remove the baffle-cap strap, withdraw the baffle-cap, and remove the interior jet assembly.
Reassemble the pump: Reverse steps for dismantling, ensuring proper alignment and securing of components.
Clean the radiation shield: Instructions for isolating the pump from the electrical supply, allowing it to cool, and cleaning the radiation shield.
Lubricate/inspect the high-vacuum isolation-valve (M- and P-model pumps): Procedure for lubricating the valve-plate seal with Fomblin RT15 grease and inspecting for damage.
Replace the pump heater(s): Detailed steps for replacing heaters in Diffstak 63/150, 100/300, 160/700, and 250/2000 pumps, including disconnecting electrical supplies and securing new heaters.
Check the heater securing nuts: Regular checks to ensure tightness.
Clean the cooling-coil: Procedure for cleaning the cooling-coil with a suitable descaler.
Adjust or replace the position indicators: Steps to adjust or replace the valve closed and valve open position indicators.
Fault finding: A table is provided to diagnose common issues like poor ultimate pressure and inlet pressure surges, with corresponding checks and actions.

Storage and Disposal

Storage: Instructions for shutting down the pump, isolating it from the electrical supply, draining the fluid, dismantling and cleaning, and storing in dry conditions.
Disposal: Guidelines for disposing of Diffstak pump and components safely, noting that components with fluid contact or contaminated with dangerous process substances require special handling. Fluoroelastomers may have been subjected to temperatures above 315 °C.

Service, Spares and Accessories

Edwards provides a worldwide network of Service Centres for support, including equipment decontamination, service exchange, repair, and testing. A list of fluids and spares (heaters, valve-plate 'O' rings, valve shaft seals, valve blanking plates, position indicator spares) is provided with item numbers. Accessories such as cooling-fail thermal snap-switches, pump-ready thermal snap-switches, ISO tube and collar assemblies, rotatable flange packs, pump inlet seals, and various valves and clamps are also listed.