Quarter the potatoes lengthwise and cut them crosswise into 1/2 inch pieces. In steamer basket, add potatoes and place in pressure cooker with water.
Close lid; bring to high pressure, then lower heat and pressure cook for 5 minutes. Quick release pressure using cold water release method, open lid, drain water and remove potatoes to bowl.
Put eggs steamer basket or egg poaching tray in cooker and add cold water to cover eggs. Bring to a rolling boil (do not add pressure cooker lid). Reduce to simmer and let them cook for 10-12 minutes. Plunge into cold water at once. Once cooked, chop into pieces.
In a large heavy skillet, cook bacon over moderate heat, stirring, until it is crisp; then transfer to paper towels to drain.
Pour off all but 4 tablespoons of the fat, and add to skillet onion and celery. Cook the mixture over moderately low heat, stirring, until onion is softened. Add the sugar, flour and celery seeds, and cook for 30 seconds, stirring often. Stir in the mustard, vinegar, and 1/2 cup of water, bring mixture to a boil, stirring, then lower heat and simmer for 2 minutes, or until mixture is thickened. Season the dressing with salt and pepper, pour it over the potatoes, and stir in the eggs, pickles, bacon and scallion greens.
Serve the salad warm.